I found that retros tend to devolve into gripe sessions when the team isn't able to change its environment. Best to keep them focused on things they can actually change, and just to let them fix what they need instead of talking about it.
Also, after an initial stabilisation period, teams need fewer and fewer changes. Talking about it every sprint gets really pointless and takes time away from the things they're good at and they're motivated to do.
But I do wonder if it just encourages people not to bring up real problems so that they can skip a meeting.
I think having the board up at all times is a great idea though. Just have to have some way to figure out "is it empty because things are fine or is it empty because no one cares anymore".
Also, after an initial stabilisation period, teams need fewer and fewer changes. Talking about it every sprint gets really pointless and takes time away from the things they're good at and they're motivated to do.