what do upgrading skills/attacks do anyway? the tooltip does not change at all.. like goblin punch does same dmg regardless of lvl from what i can see.. and upgrading doesnt change the description at all.. it would be nice if it was higher multipliers... lower time cost.. or higher chance to crit.. but if it is a higher crit chance, it would be nice to have some descriptor to explain that..
Rusty dagger, is also a dmg thing that doesnt change.. and it doesnt even have a crit thing to it.
healing doesnt change either.. so what does upgrading do? except costing more expensive mats to repair.
Once you have the orc body, taken over the village and built the library you can have Zana do research.
If you research "battle" once, then afterwards you can research your skills/weapons.
With some progress in the story (I think obtaining the goblin body again and visiting the goblin hideout) you can then see the stats of the weapons/skills in your menu for managing the setup of your deck.
There you can also see the effects of the upgrades.
E.g.: On the goblin / orc attacks upgrades increase the crit chance by 5% per upgrade.
On the throwing knives attack upgrades increase the number of attacks - probably by 1 additional attack per upgrade: Like 5 attacks + X attacks with X = the number of upgrades).
Basically:
Chance on skill --> Upgrading increases that chance by 5% per upgrade (percentage visible on different upgrade stages)
Number of attacks on skill --> Upgrading increases number of attacks by +1 per upgrade (cannot be seen on the card, just a guess from using it in battle)
No chance + no number of attack --> Upgrading increases direct damage (the increase cannot be seen on the card, so no idea how much per upgrade)
Edit:
Btw. I found the goblin / orc skill respectively to be the most efficent attacks.
They cost low action during battle and can get good payout with the crits.
Furthermore their endurance does not decrease, so they do not need to be repaired - same as with the skills you get from your companion.
So upgrading the goblin / orc skill is the most useful in my opinion as you get good damage and do not have to worry about repair costs.