To be honest with you, the only things I might change if it were mine were pickups, electronics and tuners.
Having said that, I own a Squier Affinity P and it sounds great, stays in tune, and makes no noise when turning the volume and tone knobs. I plan to upgrade the pickups to 62 reissues, but everytime I think to do it I plug it in and play it and can't justify the money.
And though I'm a beginner(not quite a year on bass), I've played guitar for 25 years, and I also play piano. Believe me, if there was something lacking in tone, build, or feel, I'd notice it. I'd love to upgrade it, but it just doesn't really need it. If i were a gigging bassist, I'd gig it right now without the least hesitation.