By the time I had my P5Q I started moving away from the mentality of buying a whole new rig every few years for thousands and settled into a groove of incremental updates. In the end, the cost is pretty much the same except it doesn't hurt as much because it's spread out over the years and you never get left with the feeling that your setup is outdated and slow.
Sometimes the outdated components you have even come back to redeem themselves. Right now I have an old Zalman heatsink cooling I bought way back for a Pentium D cooling my 1090T well (thanks to the backward-compatible AM3+ mount) and the 9800GT I replaced with a GTX 460 has returned as my secondary GPU for PhysX which doesn't come in handy for many games but it sure makes BATMAN look more awesome.
Electronics, like cars, are a pay-to-play hobby. You're never gonna get your money back from either, so I just don't see the sense in even trying to justify a purchase or worry about how much money it'll cost (within reason). If you enjoy it enough to fuck around with and consider it a hobby then just accept it'll cost you; upgrade often, and keep a monthly ledger to see what less-fun things you have in your life that you can economize on to free up funds for what you do want to enjoy.
Life is too damn short to deal with shit like low FPS, isn't it?