I still have my late 2008 MacBook Pro--the first 15" unibody design with a Core 2 Duo. I just spent about $250 for 8 GB RAM upgrade and a 500 GB SSD and did a clean install of El Cap.

It actually runs faster now than it did with the stock HD and Mountain Lion! Granted, I'm not doing a lot of heavy computing with it. For web surfing and the basics it still works great.