I see what you're saying. I think in the past I've tried a lot of activities to try and open myself up, but I think almost all of them have ulterior motives. For example, maybe two years ago I took up ballroom dancing, which led to swing dancing. I think I mainly did it to meet women, and I was never that interested in it. Even after 5+ months of dancing with the same people I never felt natural or relaxed. I still feel like there's a huge part of me that none of them ever got to know.
To be completely honest I think I mainly just sit at home and wait for someone to invite me to go do something. As I've gotten older this happens less and less frequently, leaving me in my room on the internet or playing video games (which I can no longer do due to an RSI).
I'll try to spend some time thinking about outside-the-norm things that might interest me. I'd love to hear some suggestions someone might have for looking for new things to do. I just find it hard to think of something that truly interests me, completely ignoring the practical or financial aspects of it. I'm always thinking of how I could apply the activity in logical terms.
Here's some things I've done and didn't enjoy, and the reasons:
Dancing -- meet women
Learn Spanish -- Job opportunity enhancer/fall back plan
Drink/Party -- meet people (I don't even like alcohol)
Join a Fraternity -- open myself up (horrible idea, the second I got in I wanted out)
Take art classes -- I was envious of people that could draw well
Gym/Exercise -- Make people like me via my physique (I still exercise though as it's healthy)
Two things I've always liked are mountain biking and snow skiing. Skiing is out of the question these days as I simply can't afford it. Mountain biking is fun, but it's not something I can do with other people. *Real* mountain bikers are crazy and the last time I rode with one I hurt myself, and I'm afraid of hurting myself badly by pursuing that route.