Yeah, 25c is probably narrow for gravel. Don't get anything with any major tread, though. Even slick tires of sufficient width should be fine on packed dirt bike paths and gravel. If you're mostly on the road, get a tire that suits the road and just go easy on the rough stuff.

I just rode off-road on some Kenda Kaliente 23's last week, even over lingering snow. I survived. Partly b/c I wisely walked 10 feet of the route...