I haven't heard about any drop in performance. It either works or doesn't. I recommend you clean all your system fans at least once a year with a canned air solution designed for this purpose. I use "perfect duster", one of many brands out there for under $5. Otherwise, the fans begin to turn slower and aren't as effective in keeping the system cool, including the ps. If you want to change ps, factor in future upgrades and whether you'll bother with the warranty. In general, I wait and change the ps when I upgrade the board and cpu. These brands are ok, regardless of the wattage rating: antec, corsair, seasonic, pc power and cooling, enermax, some models of ocz and xfx. Corsair usually has one high 12v rail, good for gamers. Check newegg for current specials or your preferred vender to get one of those brands for around $90 or wait until Oct-Jan for possibly better deals.
Even if capacitor aging is an affecting factor for a PSU efficiency, i don't see the drop to be by such big a margin as 30% for a usage period of less than 3 years.. This is considering a good quality PSU of course.. I don't have much knowledge on the HEC brand though.. I've a Antec True Power 2.0 550W PSU which is already a good 6 years old but adequately powers my secondary gaming rig comprising a very well overclocked Intel C2D E6750 and a single ATI Radeon HD 4870 along with all the other usual components..