@ Jonas; I think the people on this thread have contributed many thoughtful posts.
I did exactly what you’re thinking about doing. I bought a used Dell server with dual Xeons, 24 gigs RAM, and a nice disk array from a reputable refurbish outfit – ridiculously cheap.
After I spent some time setting it up, I’ve been quite happy with it. It renders quite a bit faster than my, admittedly old, i7 work station.
This older Dell server is very stable and it will run almost any 64bit OS. You don’t necessarily have to spend $1200 on a server license from MS – depends on how big your org is and what your usage is.
To my mind, it’s all a balance between $$$, immediate needs, future proofing, and support (both hardware and software). In my experience, most hardware today is fairly bullet proof. Cooling seems to be the most troublesome (fans, pumps failing). I’ve used main boards from several manufacturers over the years (including an Abit way back!) – all based on Intel chips – and have not had a chip failure yet. HDDs? Of course – they fail occasionally as do the fans and cooling pumps. Setting up a good disk array with solid redundancy is what I’ve concentrated on. I think that with today’s 6 core i7s, a good GPU, and RAM, you’re going to find you have plenty of horsepower. The traditional bottlenecks are still with storage, although I saw a video where someone hooked up 24 1 gig SSDs in a large array and that disk setup finally over saturated the processor, RAM, serial bus capacity.
On the software end, Adobe CS seems to be good and relatively stable. I’m not too happy with their decision to go with subscription based software which messed up the upgrade paths for a lot of people, but that’s the where it’s all headed now.
Considering that I spent about 1/3 $$$ on the used server (and setting up the additional redundant disk arrays), I’m set for the next couple of years. Yes, at some point, I will have to spend a huge chunk of $$$ for a system that has the latest and greatest hardware, but for now and for my specific needs, the used dual Xeon setup is working quite well.