Whilst I appreciate they keeping its value. If I were to buy a mechanical watch I wouldn't buy it hoping it will keep its value or increased in value. I would buy it like I buy a piece of art and appreciate it for what it is. Something like an Omega it costs a few hundreds to service every few years depending on model, even if it keeps its value you are still losing hundreds of pounds every few years in servicing. My car only costs £140 inc VAT to service per 20,000 miles which to me is more than 2 years driving, so by comparison it is quite cheap seeing the watch costs less than my car, (dependant on age, the contrast could be more extreme).
So I never understand the "hold its value" argument. To even contemplate that you would have to really care for it, careful not to scratch it, not to wear it while working, play sports, go to festivals etc. No doubt people will argue that it is tough and they have worn it to this and that and it's still mint. Well, I once accidentally wacked my wrist when walking pass a commercial freezer with a stainless steel edges on its corner, HARD, TWICE, in the space of 30 seconds. I very much doubt anyone would lent me their Rolex or Omega to recreate that again and see how it flares. My £200 Seiko's front face is scratched like an ice rink, it is probably worth nothing more than the price of a Nandos meal but all I've lost is £200 after 8 years of ownership with no servicing, and I do not need to adjust the clock at all, only change when day light savings intervals.
That to me is real value.
Spending £3,000 on a watch and spends £300 to service every 3 years after 8 years will set you back £3,600. To technically hold its value you will have to have it in the condition that it came in and the second-hand value for it will need to be worth £3,600 for you to break even. If it is worth the same price as you purchased it you would be in a deficit.
I would buy mechanical watches to appreciate the workmanship, like a piece of jewellery or art. Nothing more. The servicing part is part of keeping it in good working order and I wouldn't even think how much it is worth because it would not be for sale.