stock denon 103 vs. zu for my vintage rig

I'm just getting into vinyl and pondering how far to take my cartridge choice.

I've got a Pioneer SA-9800 integrated (top of the line, circa 1979) running through a pair of Magnepan IIC's (1986, I think). The sound from this set-up, at least through my Kyocera cd player, is sublime, but they vinyl coming through my Pioneer PL-50, leaves much to be desired.

This lovely table has what looks to be a vintage Pickering V15 with a newer replacement D625 stylus.

The resolution is poor to fuzzy. It could be my newbie attempt at cartridge set-up, but I do believe as well that my system would be best served by a cartridge upgrade.

Seeing as my amp is equipped with an MC phono stage, I was thinking about the classic Denon 103.

My tonearm is the original Pioneer, which I understand is on the heavyish side, so the low-compliance Denon should be a good fit.

The question is whether or not to spend the extra scratch on a Zu-modified version.

The $499 zu's are all sold out, leaving only the pricier, lower-tolerance variants. With that in mind Audio Feil's discounted Prime cartridge at $699 seems the best choice of the available zu options.

So the question is, is it worth it for me to spend about 3 times the price for the zu vs. the standard 103?

From reading around, it seems there is a definite upgrade, but a few have complained that some of the 103 "magic" has gone by the wayside.

Or is my gear not up to the challenge of delivering the best the Zu can offer?