no that is cool to mix and match...I mix my LV with Gucci and Prada...For example when I carry my Gucci boston I put my groom wallet in it and I carry either my mono or red vernis cles and I wear Prada boots...it all works and it looks different...sometimes it is nice to match and sometimes it is nice to mix it up....
I usually buy the wallet that goes with the purse but for some reason I didn't buy a gucci wallet with my purse wich is pink so I use my multicolore LV instead, it looks fine.
i mix and match designers, i use my balenciaga bags a lot. and the wallet and agenda and other misc accesories are mostly from LV, and they too come from different range. my agenda is the panda, my wallet is black MC, my coin purse is white MC.
I use my Coach wallet in any bag, be it Coach or not. I love the wallet and it was a gift from my mom, so I don't really care if it matches the bag or doesn't. I figure I wouldn't worry about whether anything else in my bag matched the bag itself, so why worry about my wallet?