If we detect radio signals in another galaxy but FTL is impossible who cares? The human species will be extinct before any interaction can occur. It's probable that whatever species sent them is already extinct because it's at least 3 billion years old.
If c is the ultimate speed limit there's really no point in looking anywhere else because everything else is so far away it's irrelevant.
We get generation ships, and if we are extremely lucky, we may have some very patient pen-pals, but warp drives, ansibles, and their attendant paradoxes are pretty unlikely to be features of this universe. Personally I prefer a knowable universe to a tourable one.
If FTL isn't possible then the end result of listening is simply the confirmation that something else exists and it stops right there.
Don't you think there's at least a little bit that could be learned by listening to alien communications from centuries ago, other than the fact that it exists?
If such signals were found, would you really stop reading at the headline "alien communication discovered"?
Who is it that's speculating about quantum communication? Certainly not physicists. It's mostly just IFLScience!-class journalists seeing a term like "quantum teleportation" and assuming that it means start trek is real and write their articles based on that.
> I believe that everyone at SETI must believe FTL is possible because otherwise it truly is a waste of resources.
If everyone at SETI believes that mysterious FTL communication exists, then why do they spend all their time looking for EM signals?