The idea behind modding a bass is to make it something that you, specifically, want to play. Unless you know what you want out of an instrument, I wouldnt bother.
Only recently, I've discovered that I want a Jazz bass with a much wider tonal spectrum. So I'm swapping out the Pre-amp for a John East Retro to try to acheive that. It's not just aimless tinkering, I have a goal in mind.
If you're trying to make this bass sound nicer for you, before spending money, make sure you actually want to play it!
Anyway, personally, I think that pick-ups change the overall sound of a bass more than anything else does.
As for playability, all you can change really is the neck. If you've got a Precision neck, but prefer the shape of a Jazz neck, swap it. Then it'll be nicer for you to play, you might play better and then you won't need to worry about changing the electrics. Perhaps!
Truckstop