The safest position is to assume the camera you buy will be worth nothing when you come sell it. Buy it for life, pay for repairs when needed, and you'll never be disappointed. Of course this cosy picture falls apart with d*g*t*l photography.
Unless you're a professional writing equipment off against tax, new cameras are lose squared. There are sufficient numbers of "enthusiasts" prepared to pay inflated launch prices just so they can go on forums and brag/complain. The price they paid will be lowered by manufacturers in as little as six months, sometimes less, so if they expect any kind of return on their "investment", they better dispose of their "asset" pretty quickly. By the end of the product cycle a camera will be for sale, new and warrantied, at a considerably lower price than those advertised secondhand. Who'd be a bricks and mortar used camera retailer with that pricing model?
The reality is someone could trade perfectly good 1970s-1990s SLRs all day long, and barely make enough money to keep the lights on. The usefulness of a camera as photographic tool, its condition and value to an individual, has no bearing on its market price. With cameras as with most things, never mix business and sentiment.