Unlike soundslikepuget, I don't think you have to go out with a group to not look creepy. Seattle is definitely a city where I see people of all ages out at shows and clubs. I'm in my late 30's and I think it would be horribly sad to stop dancing or going to shows because of what other people thought.
As for dressing up... it depends. The shows and dance nights I go to tend to be pretty casual so I think you'd look more out of place "dressing up" (whatever that means). But yeah, I'd break out the skinny jeans and v-neck t-shirt if you can still rock that look.
Final piece of advice- don't scam on the super young women. I know they're really hot but it'll look creepy and when you're done having sex, there's really nothing to talk about that won't leave you feeling old.