Hi mate - swapping the bridge on my MIM Jazz Deluxe was the first bit of modding I did - I used a High Mass Gotah bridge, which I'm really happy with. Being honest, it looks cool and was a good first step in modding, but it has made no noticable difference to sound or playability, it's just easier and sturdier when changing the intonation. I know some people who swear by bridge changes, which I understand on a Strat or something with a tremelo, but on something as solid as a P or J bass I really don't think it makes much difference. Another option which I did to my P Bass was to get a Fender Hi Mass Deluxe bridge and some ferrules - this involves borrowing a pillar drill to drill through the body so that you can set up a through body bridge, which is a bit tricky and quite bold to do to a Fender, but that really, really did make a noticable difference to the sound quality. Hope this has been some help
