I own several 70 Series, but no 80 Series but there are a lot of similarities.
The one for-sure difference is that the 80 Series has a mechanical firing pin block which prevents the pistol from firing if its dropped. Some folks don't like that, some do, most don't care. For all practical purposes, it doesn't affect the normal operation of the pistol and does afford an increment of improved safety.
Finish
There are at least two kinds of nickle finish. Don't know if Colt carried over the "satin nickle" finish into the 80 Series. If that's what you have, be aware that its very delicate and will show normal carry wear very quickly. The satin nickle finish is typically quite dull in appearance, kinda like flat wall paint. If the finish is "electroless nickle" or e-nickle, that's good if you like nickle finish as its quite durable. A typical e-nickle finish is bright and shiny. I believe that e-nickle was a premium finish available only from Colt's Custom Shop. Are you sure the finish isn't actually stainless steel. That was introduced as an option on the 80 Series and is quite popular because its durable, and can be rejuvenated quite easily if it gets scratched or scraped. If the pistol you're considering comes with the box, the finish code will be "SN" for satin nickle, and "E-nickle" or "EN" for the preferred electroless nickle. Clever.
Barrel Bushing
The 70 Series used a fingered barrel bushing that allegedly produced a more accurate pistol. There are stores, typically undocumented without pictures, of the fingers on the colleted bushing breaking and really jamming up the pistol requiring signficant professional help, just to get the darn pistol apart.
The colleted bushing was carried into the 80 Series products until 1988 or '89,
the stories vary, but its quite possible that if your candidate is an early 80 Series made before 1988/89 it could well have the colleted barrel bushing. All of my Series 70 (three total) have the collet bushing and I and a lot of others couldn't care less.
That's all I can think of that might apply specifically to the 80 Series Gvmts.
They're fine pistols.
Good luck.