Hello!
The differences are very minor and the majority of people will not notice them. Here's the main differences.
Primary difference is that the reissue has an
alder body and the original issue has
basswood body. The reissue pickups are also called something different but I've not heard anyone saying they prefer one over the other. The reissue pickguard may have a more "shiny" material in it than the original. I do not believe there are any neck differences. Someone please jump in if you have this answer.
Here's some more info to help your research.
Original specs - Winter NAMM 1996:
https://www.jag-stang.com/guitars/jagstang/jagstang-technical-specs/ Original press release - Winter NAMM 1996:
https://www.jag-stang.com/guitars/jagstang/press-release-winter-namm-1996/ Re-Issue press release and specs - Summer NAMM 2003:
https://www.jag-stang.com/guitars/jagstang/reissued-jagstang-debuts-at-summer-namm-2003/ Also if you're just having issues with fret wear and really like that neck I would recommend looking up a well respected luthier near you and get an estimate for fixing it up.
Thanks and let us know how it goes!