So, for example, Plaintiff slips and falls at a restaurant owned by Defendant. Eventually, a settlement agreement is reached, and as part of the terms of the agreement Plaintiff has agreed that she will never return to any restaurant owned by Defendant for any reason. Is this enforceable and if so, are there any consequences besides breach of contract and trespass remedies?
Is this enforceable
Yes, it is enforceable insofar as it was knowingly and willfully agreed upon by the plaintiff (you don't mention any assumption in the sense of plaintiff being deceived or coerced at settlement).
However, the remedies for breach should be explicitly stated in the contract because, from the rare nature of such agreement, it is unclear how to proceed.
if so, are there any consequences besides breach of contract and trespass remedies?
Yes. One possible consequence has to do with precluding future grievances or lawsuits by the plaintiff. The contract might be devised by the defendant to preempt subsequent litigation in the event that the plaintiff shows up again at the restaurant to stage a[nother] slip & fall, and then plead in court the cause of premises liability.