Heck depending on the board you may not even need to buy a newer machine even then, just slap in a new board. We had a power surge about 6 months ago that took out the youngest boy's board, know how much it cost for a board that supported 32Gb of RAM, crossfire and octocore CPUs? $70. We slapped in an old Athlon X3 i had lying in a drawer, took about 5 seconds to unlock it to a Phenom X4 and he has been happily playing the latest shooters without problem.
The simple fact is programming for SMP is INSANELY hard and the programs haven't even come close to keeping up with the hardware. that goes for Linux as well as i recently tested the latest PCLOS and Ubuntu and they frankly don't do any better at SMP than Windows does at this point. I play the latest shooters, Metro LL and Far Cry 3 and my 4 year old AMD Hexa with 8GB of RAM and HD7750 cranks up the purty and stays above 30 FPS throughout the entire game, so why should I buy a new system?
BTW you notice that the ONLY ones here complaining about the end of Moore's law are the ones doing jobs that frankly MAYBE 0.001% of the population would EVER do? 10bit video? DVDs still outsell Blu Ray by something like 40 to 1 so obviously the public isn't interested in ultra HD. Computational Fluid Dynamics? hell I don't even know what the fuck that is, Joe and Jane Normal sure as hell ain't buying boxes to work on this crap. Seems like a job for a grid computing solution anyway.
Like it or not the computers, including tablets and phones, have gotten several orders of magnitude more powerful while the work that the normal folks have for them has stayed the same. The customers that walk into the shop today? Have the exact same uses and problems as those that walked into my shop a decade ago. surfing, video, email, games, its the same jobs. And now that you can get quad core laptops for less than $350 and quad tablets for sub $150? Like X86 the mobile market will quickly become saturated just as the desktop market did.