Just how different are classic basses from their newer counterparts?

[ThomBassmonkey]

I have a Sandberg JJ5, it's basically an active Fender Jazz 5. Hopefully next week I'll be picking up a Fender Deluxe USA Jazz 5, so basically the same bass (active 5 string Jazz, same body shape, pickup config, 34" neck etc), but different.

I'm not thinking specifically these two basses (I'm including things like Sadowsky, Overwater etc), but in general, how much difference does the changes made make to the basses? Do they feel similar? Sound similar? Are they really upgrades to a classic model?

I don't really know what I'm expecting with the Fender, my Sandberg is a SERIOUSLY good bass so it'll take a lot of beating, but I expect the Fender will be a close second (close enough for me to keep it). I started this topic more as general discussion than a "will the Fender be better than my Sandberg" though. When I have them both, I'm gonna record some sound clips and do a proper comparison.

[Doctor J]

You'd find big differences even if you were to compare just Fenders throughout the years. I've had an ESP J4, a couple of Fender J4s and a Sadowsky J4 over the years. While they all were J basses in theory they didn't really feel or sound anything like each other in practice and I sold all but the ESP. By the same token, I've got a Bacchus J5 and a Hotwire J5 and, again, while they're unmistakably rooted in the classic Jazz template, they feel and sound remarkably different. It takes more than just a basic body shape and two J pickups for the instrument to feel the same.