If you're used to hauling your kids most of the time, I think the LHT sans kids will seem plenty fast... I pedicab one evening a week, and my hybrid, even loaded down with a couple panniers seems incredibly light, fast, and responsive after a few hours taxiing people around in one of those! Though to continue the automobile metaphor, I think a pedicab is kinda like a dumptruck, so...

As for the trailer question, TONS of tourers have pulled trailers behind their drop bar bikes w/o issues. Not sure why the first LBS seems concerned.