Yes, the roots can be a hassle. Our concern is usually a seat or trailer on the back and those blasted roots are just unavoidable. I think they improved the bridge side, not too many harsh bumps towards that end.
Chipped up glass would be an awful filler! I hope we don't have problems with that!
We are still on the new side of tandeming. Not quite a year yet and we hang the bike up during the long New England winters so we have plenty of technique to work on. We racked up the miles last year but usually we prefer hitting the roads with as few obstacles as possible. I think riding on as trail would be helpful when we are trying out a new seat or dialing in the height or things along these lines that would require frequent stopping. Just don't want the trail to be be more difficult then fun!