I build my planes gear down (sometimes I take great pains in doing everything down!) and I haven't put a plane up close to the ceiling in over 25 years now. The reason is that models, in particular paints and decals, get damaged by light and dust. After having spent so many hours on a model, I'm not ready for those two to destroy my efforts (without counting the accidental mishaps such as removing a shirt and get it caught by the pitot tube or other bit sticking out of the plane...).
Of course, it means that most of my models are boxed up and will only see the light at shows or when it's their time in my display cabinet...
As to gear 'up', well, it's always possible to do it. Most of the time, of course, kits have not been designed for that kind of display and some surgery is required, but that's not that hard work. Some of the nicest models, and certainly some of the most visualy pleasing have been models in the gear up position, artfuly placed on some kind of stick coming out of the base. Aerobatic team aircraft, in particular, can be very attractive that way, with the 'stick' camouflaged into 'smoke'...
However, there are still ways to combine gear down and have a jazzy display... Take offs and landings are spectacular times in any flights and, as far as we are concerned, usually call for a bit of challenging research and surgery...