Lots of teams grab starting tackles outside of the first round, I don't think that's news to anyone. I don't think RT is an immediate need or anything, though: Kaczur is serviceable. If anyone worries me on the OL, it's Light (good most of the time, but he gets really manhandled by some of the elite pass rushers) and Neal (injured too much).
If we ended up with a pick at the top of the first for Cassel, I'd hope that the Pats would take one of the elite LT prospects for this year, and maybe that would bump Light over to RT, but I doubt that replacing Kaczur straight-up is a priority.