Engine Oil, Any Thoughts?

I like to change the oil in the Jeep Wrangler every six months. I've heard from car people that six months between changes is a bit much, especially with the harsh Wisconsin winters. But the thing is, I think I've put on 1,000 miles since this spring. An oil change might cost me $20 but is it worth it? Keep in mind that this Jeep should last me another 20 years (putting it at 30 total). Commenter's thoughts appreciated.