No it's not cool. Any differences must be quashed and belittled imo.
weezer hasn't played "you might think" live very often. speaking as someone who just saw it live at the doheny days festival, i will confirm what the original poster said....it sounds HUGE live and the bass in particular really hits. whoever said it doesn't fit in a weezer show or get much of a reaction is pretty wrong - at least from the doheny days show - the crowd went nuts, and i was literally blown away at how HEAVY and massive the song sounded live. also, it seems to get heavier and heavier as the song progresses live....in fact my favorite song from the show.
I love both songs live, but I do think they should limit it to one cover per night.
And it's weird, the setlist says it was the first time performed.
I think it sounds great live.
The video you posted was its first performance.
Here's a perf from 9/11 (oops), not as good as the one you posted tho.