as long as it looks presentable and you feel good in it i cant see any reason why not! it is lovely to go out and get a new dress for an occasion but you end up spending a small fortune. no one will notice and if they do they're probably not worth the bother
I would wear the dress again. As others have said, the bride will have too much else to think about to remember what you were wearing three years ago and the other guests probably won't remember either!
Of course it's OK! I really doubt anyone will notice or care anyway, I certainly wouldn't remember exactly who was wearing what at a wedding I went to three years ago (unless it was something really unusual/inappropriate!)
I do find it so odd that women feel they have to buy a new outfit for every occasion, and we're supposed to be somehow ashamed to be seen wearing the same dress more than once - I bet most of the men will be wearing the same suit they wear to every wedding!
hell yeah. As long as you don't look better than the bride, she won't care
If you're bothered about your fashion credentials, make a thing of it and get some cheap but really up to date accessories. Without seeing the dress, I can't really tell what would work but things I can think of ...
if it has a full skirt, you could get a cheap net skirt to wear underneath (you could buy some netting and sew it onto an elasticated belt)
Wide belt - bright fluro colours are in too so if that works, that might be an option, or a brightly coloured ballet shrug. New Look do nice ones for very little cash.
Rather than a fascinator, which can be dated, what about a really nice hair accessory? Again, high st places such as Top Shop do lovely ones.
Have fun, after all once you've had a few glasses of the fizzy stuff, no one will give a shit. ;)