I think there will always be a reason for them to not be sleeping -- teething (which was always a guess for us anyway), cold/sickness, somebody travelling, guests coming, new teacher at daycare, etc. Life is always in flux somewhere. If he's in clearly in pain ONE NIGHT, and it's different from other nights, then do your usual, but I'd say to go ahead otherwise.
Good sleep for him is one of the best gifts you can give, and waking 2-3 times a night robs him of at least an hour of shut-eye, which he needs.
For us, I got out the iPod, and at the end of every other song, I'd go in and give a back-pat. For our first son, it worked great. For our second, me going in wound him up, so it was better for me to lovingly say goodnight and just go -- usually after 13 minutes, he'd be out. With our first, it was more like 45 minutes the first few nights.