I’m a current first year living at another intercollegiate hall, it’s an interesting experience and having two catered meals per day is very nice (the LSE halls have only one) but it’s true that the LSE population of intercollegiate halls is very small, simply because of the relative sizes of the universities (mine is 85% UCL, 10% Kings, 5% everyone else).
Don’t let it put you off though! I’ve made some great friends from UCL and Kings and I’d say that the universities don’t really form cliques at all.