I've not owned a SFII, but I have SFIII and IVs.
The biggest difference to me are the pickups and the neck.
The pickups can't be beat in vintage models. Period. The reissue pickups are nice, but they don't compare with vintage HB1s or mini-hums. If the reissue is from '98 or before (I think that's the cutoff), it might have SD1s which are much better than the later-made Fender HB1s. The SD1s also appear to be the same size as the original HB1s, so you could drop a pair of vintage pickups in there if you wanted. I only know because my recently purchased '98 SFIII has these.
The necks are a bigger deal to me. I've owned two 70s starfire IVs. Both had 1 5/8" necks that were *very* tiny in my hands. The '76 was better than the '73 which was so small I just couldn't keep it. All of the reissues I've played/owned have had 1 11/16" necks with a bit more heft to them. Not Les-Paul 50's necks by any stretch - more of a recent Strat C-neck if that helps.
The vintage guitars will likely be Lacquer. I love lacquer. The reissues are Poly. Looks great, but doesn't age or feel as sexy as lacquer.
As I said, I've owned many Starfires, and I opted to keep the reissues. Even with the superior pickups, sound and feel, I just couldn't bond with the tiny necks, and brother, those were some dead sexy guitars to let go!
I currently have three late 90s Guilds: Starfire III, Starfire4 and X170T. I love 'em all. I have no regrets about selling my vintage Guilds. If they had wider/bigger necks, I'd have kept them.
I'm curious what bad things you've heard about the reissues? I've never heard a bad word about any Guild other than my own whining about the Fender HB1s.
GAD