its a difficult decision to make. The offer you got is above market and if you would try to sell it in a year, you would be hard pressed to get anywhere close to that amount.
When I sold my 79 Airstream Excella Moho, I immediately regretted it and bought a 345 within hours of the new owner picking up "Lizzy".
They get under your skin, despite the ever so long list of problems and maintenance nightmares. Every trip was a challenge and worries about the engine/transmission became to be a "normal"..
I switched to 1993 34' trailer that resembles your Moho in color and size and comfort. I have a new Tow vehicle and can fully concentrate on being some 54' long , instead of worrying about the mechanics blowing up any minute.
Its a very comfortable ride, with an A/C that actually works and safety features like Airbags and escape routes that are more in tune with today's congested roads and texting drivers.
I always look for the next Classic Airstream Moho for sale and currently I am restoring a Class C London Aire, which is all aluminum.
So the passion never seems to go away and some day just the right classic will come along and I will buy it.
Whatever you decide to do, try to have your next Airstream within reach, because you will miss it a lot.
Wishing you the best of luck