My spontaneous trips involve knowing when I'm starting and knowing when I'll be home. Every little town has something interesting, even if the local people don't think there is anything there. There are fire towers to look out from, rock exhibits, corn mazes, farmer's markets, ancient churches, places to park by rivers to watch men fish...backed by interesting stories. These are as interesting to me as major art exhibits in metropolitan areas. When it's time to eat l always ask where the best mom and pop restaurant is that all the local people go to, this is where the best food is and the waitress knows all the regulars that come in, if you're lucky you can overhear conversations about the latest news from the farm, etc.
Because this is MY plan, I only do these weekenders with someone I know who's willing to wing it the same way as me. If the person I'm with causes me to stop in stores, stick to the main roads, etc. I get resentful.