I think the hybrid technique you've been using is a great idea. When I plan tours (and I use the term loosely), I try to arrange it so at the end of the day I'm somewhere there are multiple camping options. This way, if I don't like or can't make it to the place I actually want to go, there is probably someplace else I wouldn't mind going.

This has bitten me once. I ended up doing 110 miles across a mountain range. My original plan was to stay someplace just after the summit of the pass. However, I was low on food so I opted for the last campground because it was fairly close to town (and food). It ended up being closed.

By some weird thought process, I decided it would be better to ride the hilly 50 or 60 miles home rather than stop, get food, then ride the four miles back uphill to the first one that was open.