Oh my. Computer technology gets outdated so quickly and the stuff at the top of the line always tends to be cheaper compared to the price of top of the line stuff from years back. Remember how just a few years ago it was very common to see maybe $5,000 computers advertised, and that wasn't the best stuff? Now I'd be hard pressed to spend more than about $2,000 on a computer and get any more use out of it. I don't think anyone would stick with one for the rest of their life because someday in the not-so-distant future something 10 times better could cost you a small fraction of the price of what you picked up years back.
I guess I get what you are asking, though. Gd, that is a toughy. If you are going to keep it for all of the foreseeable future, I'd get the best one you can. Just be sure it is the most worthwhile upgrade you can make for the money, and consider that it will become outdated at some point. That's all I can really say.
Maybe the only useful digital technology that's lasted a reasonable amount of time is the ADAT lightpipe. So I try to get gear that can interface via ADAT.
But just because it has lasted ten years or whatever doesn't mean it will last ten more. I'm pretty sure stuff like USB and FireWire will be way obsolete in ten years. Who knows what conversion will be in ten years, we've already exceeded the useful resolution of digital conversion, but you know the equipment manufacturers want to sell new gear
I bought an RME Multiface nearly 4 years ago and in Sept. I'm buying a new comp. The Multiface will be going into it....so I'll be using it for 8 years. I have absolutely no doubt that it will still be running flawlessly 4 years from now.