Well, just rebuilt my non-steam-machine. If I were ever to buy a Steam Machine this would have been the time.
As usual I made no effort to be 'cutting edge'. In fact I was perfectly happy with my very far out of date machine until it ate the motherboard, so I targeted a a new to me machine that is way stronger than I had, but cheap. Motherboard, processor, and memory-$275. I replaced my vid card not too long ago for $50 so didn't get a new one.
I'm well under the cost of a new generation console or Steam Machine, can play all my old games which 'max out' as far as hardware requirements with Skyrim I guess. I never felt constrained with my old machine so I'm sure I won't feel limited now. I'm not sure, but I think the attraction of brand new consoles and cutting edge gaming rigs must be for multi-player gaming...or maybe just a reflection of 'bigger house, fancier car' syndrome. I've hardly ever picked up a game and looked at system requirements and thought 'I can't play this', and I've never been anywhere near the cutting edge.