Personally I use gallery only after finishing the game, first - my canon playthrough/main girl route. With gallery I check whether I missed some content with a girl or not. The same after finishing other girl's routes. It would be really great if we could for example filter in a gallery particular girl (at least when it comes to 8 mail LIs), all other girls can be tagged "Others" or smth like that.
As for walkthrough - it's cool to play blind, I do it sometimes, but, it's so subjective. I mean what can be obvious for you - is not for me, and vice versa.
For example I play the game and want to get on a girl's path, while interacting with her I have choices - gentle/romantic OR rough/jerk options, naturally I would go with 1st option, but, apparently - I had to go with more jerk-ish choices cause the girl likes it rough. You see, so when you establishing possible choices. you as Developer already know what type of a personality LI has, because you created this character, unfortunately not all players can read between lines while playing. It's a bit rough example though.
So, yeah, personally walkthrough kinda helps me to choose an approach at least with some characters at the beginning.
Damn, I am reading now what I just wrote, I hope I didn't confuse you even more with my explanations hahah.
I just woke up and got a coffee, it should get better in a bit)