I'd rate the early-'90s, forged frame guns as more desireable and more valuable than the later, cast-frame guns.
The cast guns aren't much different from a Para, and worth about the same with similar features.
I'd pay more for a really nice, forged gun than for, say, a new RIA.
Forged frames have a separate plunger tube, while the cast frames have integral plunger tubes.