I'm still using an old Core2Duo (2.53 running at 3.8). It *only* has 4GB, but I put in and SSD and an ATI 6770 a couple years ago. Does everything I need, the only things it has problems running are recent games, not a reason to upgrade in my case. Many components got upgraded from machines found in the trash.
I applaud you, sir. An evening of tech dumpster-diving with a friend of mine some time back was a real eye-opening experience, particularly where we found some office or government building chucking mass quantities of "older" equipment. Tons of working, capable silicon, heading for landfills, when a lot of it maybe a year ago would have been tempting on newegg. There was a time when the latest OS or application release would make your hardware seem terrible, prompting you to pine for an upgrade, but not any longer, with the narrow exception of cutting-edge games, or professional apps for which you should get your employer to pay for anyway.
What you miss out on with older hardware is size and power-consumption. If performance is not your goal, then with modern gear you have the opportunity to build a silent, fanless system and/or an entire PC that fits in a 5" square box. It surprises me that this remains a niche market for do-it-your-selfers or small shops online. It would be worth it to me to pay a few bucks for a noiseless rig that fits on my desk. But as long as my older rigs are running fine, no worries.