It has to be a big NO. This is premised on the fact that their appearance will have no value neither is it likely to sway the voting patterns. Judging by previous elections, it's clear that our preferences are skewed towards tribal conglomerations and that isn't about to change.
As a breath of fresh air it would be prudent for them to take a break and give their opponents a chance. In most of these debates, the candidates undergo extensive rehearsals, sticking to premeditated messages and actions that it would be hard to deduce important parameters that may sway the perceived undecided voters.