This is a total personal thing, you should probably ask him what he wants specifically, or have him do research on these things. It may be easier just to get him another guitar, they are kind of like guns...you can't have just one.
Opinions are like assholes, everybody got one.
With that being said, I did a pickup swap on a Roadworn Telecaster (Mexican) with Tex-Mex Pickups...I swapped them out for handmade Lollar 52's and the difference is remarkable. I also swapped out the saddles with compensated brass and had a bone nut cut for the guitar and had a pro setup (not some Guitar Center cretin) done by an extremely qualified luthier (one of the best techs on the West Coast, serious...the dude is practically famous). It's a fantastic guitar.
I play through a Fender Princeton Reissue. I have a few other guitars as well.