I know that in 1997 the Rialta no longer came with the bulletproof 2.5L 5 cylinder VW engine. In 1997 they started putting the VW VR6 v6 engine in the RV to get more power. I can't speak to the V6's reliability but I know the earlier 2.5L 5 cylinder is a great engine! Only the 1995 and 1996 models had the 2.5L engine.
Also, I know some people say that a Rialta that is not equipped with an onboard generator is less valuable. I say PHOOEY!
What I have found is that most Rialta owners absolutely HATE HATE HATE the onan and generac onboard generators that came with their Rialtas. Onboard generators are loud, smelly (exhaust fumes) and vibrate when running. Many owners actually remove their onboard generators permanently and use the cubby for storage space or for housing a portable generator.
My Rialta did not come with the onboard generator option. I bought a small portable 1000 watt Honda generator and use it to power everything except for the roof A/C… which I never use anyway! A small portable genrator is a better option in my opinion, because they are more efficient (using less gas), they are very quiet (52dB at full output), they don't emit a lot of exhaust fumes and you can place them 100 feet away from your RV (when boon-docking)! At 52dB and 100ft away, you will barely hear it running, you won't smell any fumes and it won't vibrate your Rialta!
So, did you end up buying a Rialta yet?
I'd been searching for a while and found out quickly that the Rialtas are very expensive but they are worth it!