I haven't seen any pre-production photos or illustrations of the new motorhomes yet, perhaps someone else knows where that info can be found. I'd have to say that it's doubtful that your '88 345 will appreciate quite that much or that quickly. You'll probably see the prices rise for the older Classic motorhomes though, as the new ones make a splash, and folks decide that they want one, but can't afford new. It will infuse new buyers into the used MH market. Supply and demand takes 'hold, and prices will rise.
Before the 'reintroduction' of the Bambi, I bought a '61 Bambi in OK shape in 1998 for $1100 and the owner was pleased to get rid of it for that. After some repair work, and using it for three summers, I sold it in 2000 for $6000. I could probably get around $9000 for it today. The demand for original Bambis is high. Motorhome demand doesn't seem to be quite as high as for vintage lightweight trailers, but I suspect you'll do OK with your '88 over the next few years.
AIR 2053 Current: 2006 Born Free 32 RQ Kodiak Chassis, & 1995 Coachmen B-van
Former Airstreams: 1953 Flying Cloud, 1957 Overlander, 1961 Bambi, 1970 Safari Special, 1978 Argosy Minuet, 1985 325 Moho, 1994 Limited 34' Two-door, 1994 B190 "B-Van"