Is it worth a six hour round trip, to go to Lourdes.
Only you yourself can answer, as we know nothing about the depth of your religious beliefs & piety.
If you're a devout Catholic, it's probably worth it. But I found it to be severely commercialized, and to me as a not-very-religious person, a disappointment.
If it's a place you are really interested in visiting, I think it is worth it. I agree with Tom that the town of Lourdes is extremely commercialized and disappointing. It's a conglomeration of souvenir shops selling everything from bic lighters to swiss army knives, all with an image of Our Lady of Lourdes. It's so bad, it's funny......But the site itself is quite impressive and respectful.....Just don't plan on spending time in the town itself.
I spent 4 days in Lourdes a couple of months ago. If your interest is spiritual, I would definitely go. While it's true the town is commercial, once you enter the domaine, that stops[INVALID]it is absolutely protected (and quite large and beautiful). I was surprised how powerful those days were and still are[INVALID]I wasn't expecting it. Even the liturgies in the underground basilica (which holds 10,000, I believe), were conducted with silent reverence and were very beautiful (and I usually am distracted by crowds). If I go back (and I think I will), I'll avoid weekends (or at least popular weekends... I was there for their mother's day, which got a little distracting in late afternoon). And as an aside, I traveled by train from Paray-le-Monial (near Lyon); 10 hours, but a very pretty ride... down through Provence and along the Mediterranean before heading north along the Pyrenees.