Never buy another nose-hair trimmer as long as you live!” “The last dry-clothes folder you'll ever own!” “You'll never need another software synthesizer!” Whoa! Roll back and play that last one for me one more time.
I've actually heard claims about synthesizers (hardware and software) and other products that are very similar to that last statement. At the time I heard them, I said to myself, “Self, that's just piffle!” And, of course, it is.
Software is the soft white underbelly here; it will always need upgrading, at the very least. But developers also will continue to create juicy new products having capabilities that will first be desired, then acquired, then required. To the degree that your studio or rig is software based, you must figure on an ongoing expense stream just to keep it sufficiently current.
That is not to say, however, that you need to go for every upgrade or decent replacement that comes along. The bottom line on equipment value is how useful the product in question is to you. No matter if it's new or old, if you use it a lot and it gives you what you need, it is worth retaining. Many people still try to run Digidesign Sound Designer II and Opcode Studio Vision — two programs that, for all intents and purposes, shuffled off this mortal coil years ago. Clearly, some people find these tools useful enough that they would unquestionably purchase an upgrade should the opportunity be presented.
There will always be some new tools providing “Oh my god — it even bakes my sweaters for me!” functionality, and they will justify your parting with some hard-earned filthy lucre. Similarly, there will always be those tools that would be nice to have but that you can't quite see dropping the bucks for.
Hardware, interestingly, can sometimes maintain its value longer than software. Emulations of classic compressors have gotten quite good at capturing the essence of the original. The authentic analog hardware, however, often has that last little bit of magic that initially set everyone raving about them. I don't see too many people dumping their LA-2As on the market, and I keep a Mac Centris 650 running just as a chassis for a Lexicon NuVerb card because, as good as plug-in reverb has gotten, NuVerb sounds better than most of them and doesn't tax the CPU.
On the other hand, some old Tapco mixer somewhere was just laid to rest last year when a control surface took over the mixing duties.
In my “O”-pinion, the best candidates for retaining value over time are transducers. Properly cared for, a good microphone or speaker remains for many years as useful as when it was first purchased. Technological advancement happens, but the rate of change is much slower for transducers than for software. That's because the laws of physics, which don't seem to change all that quickly, rule more directly and heavy-handedly over information transmission. Energy conversion is a tricky business, especially when carrying information, and the result is that each designer's vision of transduction produces a different sound. Character shows itself as the most compelling sonic reason for choosing one transducer over another. And as long as we live in the analog world, we are going to be dealing with transducers as the first link in many signal chains.
So, is it forward to the past? Stock yourself only with the good old stuff that will still be around in five years? Or should you stay on the cutting edge and bite the bullet on upgrades and, eventually, replacement? There simply is no right answer to those questions. The answer to them all depends, obviously, on what type of work you're doing. My advice is to make sure to recognize where value really lies for what you do. Don't think that you'll never need to buy another computer, any more than you'd think you'll never buy more nose-hair trimmers. Of course, if you use good mustache scissors for a nose-hair trimmer, you're set for life.