Just won this old Robotech Revell Model on Ebay? Should I or Shouldn't build?

I would just build it and (maybe ) enjoy rather than hang onto it in the hope it  might increase in value...

It might increase in value, but...

• The anime series from which it came, Orguss was (sticking my neck out here)  pretty obscure and somewhat overshadowed by other series (like Macross) which were around at the time. It's likely to be only of interest to die-hard fans of the series.
• It's Revell boxed, rather than boxed as an original (by Arii) item from the series, and so will most likely to be only of interest to die-hard fans of the series, who couldn't find an original boxing.
• It's already long out of production and likely to be only of interest to die-hard fans of the series.

Just because it's an old kit and out of production doesn't automatically mean you're (maybe) sitting on a goldmine.

Edit: - Just located an "original boxed" version of this kit on Evil-Bay. The Buy it Now asking price is $55.00  - so you seem to have got a bargain. (or the Revell rebox does make that much difference.)