I'm looking to upgrade from my late '09 Pro. I use it to run specific light-weight software (think word processor level) and it's not my daily driver. However, it's maxed out at El Captain, which means it's useful life with me is over, as I need something that can run Sierra. It's irritating as the '09 runs the software I need just fine, but the newest release requires Sierra, so the writing is on the wall. Since it's not my daily driver, I'm looking at used. What should I be looking for that is a decent mix of remaining useful life and value? I'm willing to spend up to around $1,500 (give or take), but would prefer to keep it around $1,000. 13" or 15", don't care about Retina or Glossy, but would prefer to avoid a crummy keyboard and lack of ports.