Interviewing After Accepting an Offer?

Hi all,

Want to know your opinion on this. I recently signed an agreement with company A, but received an opportunity to interview with company B because they got back to me late. I don't plan on reneging, but since I may have interest in company B further down the line, should I just go to the interview anyway to network?

My thinking is if B gives me an offer, I'll turn it down and tell them I've committed somewhere else (and ill have a good rep if i re-interview FT), but even if they don't, I'll have one or two contacts at the firm for future reference.

Would appreciate any any all advice.