I love sharing knowledge with other 'horse' people and I think you learn a ton that way! Even if you have different ways of doing things you never know when someones suggestion might come in handy - or, when you're stumped you might need someone to turn to! There is a fine line between being choosy about friends and being a downright snob! Frankly I've never had enough money to be in the 'snobby' horse circles, so most of my barn friends are usually very welcoming! (I hope no one takes this the wrong way, but I think you know what I mean)
Of course, we all have experienced the 'know it alls' or snobs but I'm really good at the 'nod and smile' 'nod and smile' technique, just let them talk and never let them know what a pain in the *** you think they are! ;) I think when you exile yourself you limit yourself a lot and if your SIL and MIL won't let anyone else around it's their loss (too bad you have to suffer as well).