for me, with my perspective tainted by the boat industry, I find RVs are much less price sensitive to size. Once you settle in on a manufacture/model, the prices for the various floorplans and lengths are not too different. Contrast that to a boat where the price can jump 30% to add 2 feet of length.
In an RV, there is almost as much stuff in a 30' coach as there is in a 36' coach, just add some more cabinets, walls, roof, floor, and chassis length. The main cost jump I saw was the second AC and 50 amp service.
For drivability, admittedly I drove my first RV an hour before signing the paperwork, so I don't have a long experience, but an 8' wide, 12' tall vehicle is big, regardless of length. Unless you are comparing 10 - 15 feet differences in length, I don't think it would effect me until you get to close quarter maneuvering.
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