I changed the bridge on my BB614 to a Gotoh I got from somebody on here but by the looks of things, the bridge on yours is fairly chunky. Otherwise, Yamahas are pretty good.
Change whatever you don't like but - as the old saying goes - if it ain't broke, don't fix it. Plus on the whole, modified basses (like cars) tend to be less desirable than original ones. Don't spend more than the bass is worth, you'll never see the money back.
If you're looking for a project, you might want to think about "pimping" a P bass. Either get a Mex P or Jazz and get hotter pickups and new scratchplate or buy on the cheap SX copies that people on here rave about.
Good luck - and tell us what you do!