As my regular readers will know I possess a Canon XT. I've had it since it was new for which I paid probably $800 - $1000. Today I looked at the secondhand market and eBay seems to be selling plenty XTs for $45 or frequently less. Considering I have taken less than 10,000 photos using my camera over the past 10 years, it works out as really rotten value. In 10 years, had I used film, I would have taken less photos and been more mindful of the cost of the photo. That's not hard to do either. I haven't taken any photos for several months with my XT. I've taken a lot of photos with my phone though.
Checking my phone, I've taken 42 photos this month so far and that's a low number. I expect when I work on my bus project tomorrow I'll take a further dozen photos. My phone is something I need anyway and the camera on it was free. Currently phone cameras are way better value than DSLRs.
Looking at the resale value of cameras - you will certainly want to sell your camera at some point in order to take advantage of later developments - they're a huge money pit. Back in film days when cameras didn't change much from decade to decade they retained their value. That meant it was worth buying a camera because it could be reliably sold for about 75% of what it cost. Now because cameras and lenses are overproduced and oversold, the resale value is negligible. $1,000 for something that'll be worthless in a few short years is a pointless waste of money. Better to stick with a cameraphone and just agree that it won't be great for the more specialised photographic disciplines.
Secondhand, it's well worth buying a camera. The technology won't be the latest but if you can live with that, it could well be worthwhile. I'd like to take night sky photos but am stuck. I either have to spend $300-$400 on the cheapest suitable lens, $300-$400 on a camera with an ISO high enough to use my existing lenses or $175 on a secondhand camera and lens from one of the newer mirrorless systems. It looks obvious - sell the existing stuff and go for the mirrorless solution. There's a problem though - the mirrorless cameras have slightly less dynamic range.
I can honestly say that the way Canon has overproduced and oversold their cameras and lenses is exceptionlly shortsighted and has quite probably ruined the market. I know for sure that if the rate of release had been a lot slower - say one camera every 5 years instead of every 18 months and cameras with real differences rather than notional differences then the bottom would not have fallen out of the used camera market. What difference is there between the XT and the XTi? Simple - 2 megapixels. That is so negligible it's not worth mentioning. What is the difference between 8 megapixels and 16 megapixels? Not much - the extra 8 sounds phenomenal but in actuality means nothing. You will not see a difference on a 10x8 print nor on a 20x16 print.
As a consequence of Canon's overproduction and overselling, the market has been utterly ruined for new cameras. Who on earth is going to buy a new camera when they can buy a secondhand camera that's had hardly any use for peanuts? If I went for a mirrorless camera then I'd get secondhand and certainly not new! Indeed for the night sky photos I'd like to take, it might even be worth buying a secondhand mirrorless then simply selling the Canon stuff due to its redundancy. Honestly, I just can't see how the $300-$400 cost of a wide prime (even a budget model) can be justified when the mirrorless equivalent is so much less. In terms of modern technology, even a $175 camera comes with higher ISO than my XT and a zoom lens that's almost as fast as the budget prime.
Buying a camera, these days, is pointless unless it has WiFi, Bluetooth, GPS and NFC built in. It's equally pointless to buy a big camera when the market is clearly favoring smaller cameras. Its certainly not possible to get smaller than a phone camera! So, the question is - how is Canon etc going to manage to sell their overpriced junk? Seriously, if the camera is going to be worthless in 10 years or 5 years then what's the point in buying it? Better to spend the money on hookers and have some value out of it! I certainly don't feel I've had good value out of my Canon camera. And before you go on about my needing to use it more, I've had a phone camera for 3 years and have already taken 6,000 photos with it. That's way more than my DSLR in 10 years!