I still have mine. It was a simple ivory bridesmaid's dress, so it didn't cost much relative to a "real" wedding dress. I never had it cleaned after the wedding or anything. It's just hanging in the hall closet, but it's not bulky at all - no more than a regular dress. I haven't really given it any thought, but lately my DD has been asking to see it. I'll probably keep it and let her play with it.
My sister and I used to play with my mom's dress, which my grandmother stored at her house. But then my grandma gave away the hoop skirt that went under it, and then it wasn't so much fun anymore. The dress is still around somewhere, I suspect at my sister's house. We both planned to wear it for our weddings but it was just too tiny in the waist, with a gazillion buttons up the back. No room for alteration at all.
I am starting to feel burdened by all the stuff we have and it is a long process letting things go that have been handed down to me - so OP, if you are "done" with your dress, go ahead and donate and don't give it a second thought!