Furthermore, I kinda have always fallen into a hybrid of the 1) - 2) system so I can upgrade *something* every 2 years instead of 4 and still save money overall while also collecting a larger pile of spare parts to build extra lower-end boxes.
When building a new system, I typically get the best motherboard I can, and the cheapest half-decent CPU available for it.
Then in two years after the CPUs have hit the market, I'll throw in the second-best CPU available for that motherboard (the first-best usually still carries a premium). Bonus points for finding something off of Craigslist.
The most recent time I did this was pretty nice... I went from an Athlon II X2 (with 1GHz HT2.0) to a Phenom II X4 (with 2GHz HT3.0), which doubled the memory bandwidth. So even though the core clock went up less than 50% from 2.2Ghz to only 3.2Ghz, I ended up getting more than a 100% improvement in frame rates for my games, even the single-threaded ones that couldn't make use of the additional cores. And the poor sap from Craigslist that I bought the Phenom II X4 system from had it in an older motherboard that only supported HT2.0, so he was missing out on the extra memory bandwidth. I put my old CPU in his motherboard, so that's a better match now.