Suggestion: New PA job type, Accountant.
Instead of a flat 5%, change bank deposit interest rate to equal the skill level of your accountant. So no accountant, no free money, but at max level 10 you are now making 10% per year.
Also reduces company overhead by 2.5% per level as well. This means reduced month expenses for owned offices, studios and - most importantly - websites. So at max level you'd save 25% per month on these currently flat-rate expenses.
Suggestion: New PA job types, Trainers.
Remember back when Lena raised Sex Stats for your models? Same idea, but now done differently. One trainer class per skill of Fitness (Jenny's old job), Intelligence and Sex (Lena's old job). New titles for Coach, Tutor and Therapist, respectively. Each trainer has a 1% chance per trainer level per day of raising the respective stat of all your models by 1 point, up to their Potential limit. While that's only 10% per day for even a top level PA, it still shouldn't take more than six months to a year to max out every model's Potential. While that may be more expensive, in the long run, than conventional training the perk here is that it doesn't take them out of action while they're improving. They'll still be available for photos, films, etc, while still leveling up their skills.
Suggestion: New equipment class, Servers.
Just as there are five grades of cameras and lighting, so why not have the mall offer five grades of computer servers in progressive levels of expense and power? Better servers would allow higher levels of Network Quality (and the options that unlocks) without having to carpet bomb your staff list with twenty fucking webmasters (like, seriously?) Each level increases your NQ by 10%, so shelling out the $250K (or whatever) for the top tier model would take you straight to 50% by itself. Larger short-term cost but much cheaper in the long run due to reduced staff needs.
Suggestion: Online recruitment.
Each 10% of Network Quality increases the odds of your PA put on Talent Search to find a suitable model by 2.5%, so a max level system would make their jobs easier by 25% because now the girls are coming to you and applying online to join your company.
Suggestion: Different drug types.
Blow/Cocaine - Already in the game, continues to increase Chemistry by giving the girl more energy. Expensive, $100 per hit. High chance of addiction.
Crack/Yep, Crack - "Because only in America could there be some asshole who thought that cocaine just wasn't good enough." But it's way cheaper than coke, similar effects in that it increases Chemistry (but not as much as coke does) and is way cheaper ($10 per hit). Even more addictive (second only to heroin) and lowers Fitness and Beauty over time, same as Meth (see below).
Weed/Marijuana - Lowers a girl's chemistry for the day but also increases her happiness by 10%. Cheap, $20 per hit. Good for getting them back into action faster. Low chance of addicton.
Ecstasy/MDMA - Increases a girl's Likes by 25% across the board for the day, allowing her to do scene types that she normally wouldn't. Cheap, $20 per hit but has high chance of addiction.
Junk/Heroin - "Why would you do this?" As above, but increases her like by 50% because now she doesn't care anymore and will do anything you ask. Downside is Chemistry per scene drops 10%, addiction is all but automatic (90% chance per hit). Also permanently drops Fitness by 1 point per hit (at zero they die). But hey, it's cheap - $10 per hit because you're buying the cut crap.
Booze/Alcohol - At least it's legal (no chance of police action). Increases likes by 10% but also reduces Chemistry by 10%, and increases her Happiness by 5%. Very cheap, only $5 per "hit" (you're not buying the good stuff, here) and addiction is... interesting. Starts off almost zero but odds increase with each consecutive day of use. In other words, be sure to let your girls dry out livers once in a while unless you want to turn them into permanent alcoholics.
Meth/Methamphetamines - Again, "Why would you do this?" Like coke, but cheaper, increases Chemistry per scene ("so much energy!") and for only $10 per hit (you buy the really crappy stuff). Highly addictive and every ten hits taken lowers both their Fitness and Beauty stats by 1 point each (and again, they can die if their Fitness hits zero).
Suggestion: Add in new a Addiction mechanic as well.
First, an Addict has a specific thing (or things) that they're hooked on. Every day they require one dose of whatever that is to be functional, otherwise penalties are incurred (see below).
Second, add your drug stockpile ("stash") into a window that can be easily accessed. So long as you have the drugs that an addict needs, their per-scene cost drops by 25% for that day because you're feeding their habit for free (well, free for them). The downside is that if you can't meet this need of theirs then their Happiness only recovers at half normal speed (because they're paying out their own pockets and thus don't feel very motivated to do porn stuff after working eight hours at their day job to feed their habits). Also, bigger stashes tend to attract cops. You have been warned! (but remember, booze and weed are legal in most places, so if you stick with that then you shouldn't have issues).
Third, models can be addicted to more than one thing and their effects are cumulative. Ergo, that street whore who is addicted to booze, blow and heroin will do their scenes for only 25% the normal rate if you can provide them with all three that day. Of course when your stash runs out they're only recovering Happiness at 1/6th normal speed, so don't expect them to be particularly productive. But again, for the truly scummy, having a stash of cheap, highly addictive drugs (booze, heroin, crack and meth) and you're basically getting your street whore to work for (almost) free - and they'll be so high that their scenes might actually come out halfway decent... at least until they die of overdoes.
Rehab must now be done per addiction, so fixing up these troubled ladies of the night might prove rather costly and time consuming for those more philanthropic types.
Suggestion: Staff buildings.
For example, a Staff Cafeteria (raises Happiness recovery rates), a Medical Office (increases Medical Advisor effectiveness and lowers the cost of medical related actions), Employee Lounge (just like the cafeteria, raises Happiness recovery), Day Care Center (lowers child support costs), Post Production Facility (increases editing time but also increases overall quality of the final product), Reading Lounge (1% chance per day of a random model gaining 1 point of Intelligence or Sex Skill), Swimming Pool (this has a 1% chance per day of a random model gaining 1 point of Fitness - yes there is already one in the game; maybe they can be merged?), Employee Housing (rooms assigned at the staff & model info screens - can be built multiple times). All big investments, $10K+ each, but long term gains as well.
Employee Housing I think needs more explanation. What you do when you purchase this is buy one room in a nearby area (apartment, condo, house, whatever). You then select the level that you wish to purchase, up to level 5. You now have one room that can be assigned to any staff member or model. When assigned, their salary or per scene costs drop 5% per quality level of the domicile, up to 25%. The building itself will probably cost you at least $10K per level, but if you're playing for the long haul, this can actually save you money - especially with top tier models and max level staff members. Overall upkeep should be fairly low (you're only paying taxes now, since you own the property) to make this sort of investment worthwhile. Upkeep is also subject to Accountant cost reduction perks, as above. About $500 per year per quality level per room is about fair (so $2500 per year per level 5 room), and is still far below what you'd actually save in salary expenses (especially considering your average level 10 staff costs you over $3000 per month and top tier models often charge you over $2000 per scene).