Ok, given the new, revised topic of what used equipment best holds its value (new equipment will never hold its value, as like a car, once out the door it depreciates immediately), can be used for a while, perhaps a few months to a year and can then be resold for virtually the same price paid:
I recommend that units that require little maintenance (which rules out most tube amps, except preamps, as the tubes last for many years typically). You can buy the tube amps, and they do sound great, but if you have to replace the tubes, it can cost hundreds, perhaps even thousands of dollars, and you are in this to get a free ride as it were, so I recommend against it.
Therefore, I recommend:
Good solid state amps and preamps, including Mark Levinson, Krell, etc...
Very good tube preamps, such as Audio Research, Conrad Johnson, etc..
I don't really recommend :
Turntables, (The cartridges do wear out, and the arms can show signs of use very quickly. If the table is made of acrylic plastic, as so many are, it shows signs of age quickly due to dust being wiped off, and scratching the plastic! Wood can dry out and look aged as well.) But if you insist, I suggest such TT's as the high end SMI (TNT, Aries) or the Basis Deput, or other similar units.
Speakers, but only the highest value, and they need to be in the very best shape for the lowest possible value, as they also double as fine pieces of furniture, such as the Avalon Eidolons. (For some reason, speakers seem to lose the greatest value once taken out the door. They seem to lose 1/3 of the value immediately, and after only a few months, it is not unheard of that the speaker value is down by half. (I know this for a fact, as I was watching the price of the Avalon Eidolons, and Revel Salons and Studios before I purchased my Studios for 1/3 off, and they had not even been taken out of the boxes - in fact they were still sitting at the store, when the new owner sold them to me).
Any cables at all, as they seem to make so many different models each and every year, that after only a year or two, the names start to lose their luster. The caveat here is that if you only keep the cables a short while, you probably can do A/B testing to see which ones you really like. (I bought a less than one year old pair of high end MIT 770 CVT speaker cables only a year or so after they were discontinued, for less than a 1/3 of their normal retail price.)
Digital source components. I recommend against them just for the fact that they seem to be upgrading the technology constantly. The better units do seem to hold their value somewhat, but even those do start to lose value if their own company comes out with a better unit. However, some units, such as the Sony 777es Cd/SACD unit does buck the trend somewhat, although even that $3000 unit can be had for almost half, but it does not seem to be dropping much lately. Other units from Levinson and other good manufacturers also come to mind if you must indulge.
Words of Advice: If you do decide to do this, you must put in your due diligence. You must be constantly scanning all the available used sources, such as Audiogon, ebay, and the used stereo shops that also are on the internet. In this way, you can pick and choose the best available deals, and know what the prices of the different units are actually going for. Don't get hung up on any one piece of equipment, but create a list of items you are interested in and if a real deal shows up, jump on it. You'll find that it will usually be at an auction that this occurs, just because it slips through the cracks. This is exactly how I put together virtually my entire system. I wish I had the money to try what you are attempting, but I have a wife, and a strong desire to remain breathing!)
Remember also, the shorter the amount of time you hold onto a unit, the more value it retains.
Good Luck!
