My panels lost tension, I think?

These are a set of 10+ year old Scenarios.
I just decided to poke at the membranes with a thin plastic stick. It seems they deflect easily, e.g. 1+mm with very little force. Hard to quantify, but it feels like "just enough to keep things from wrinkling, but not taut or bouncy".
From reading various guides, it seems like the tension is just maintained by trying to pull laterally across some adhesive. So I wouldn't be surprised if after a decade, either it slipped a little bit, or the mylar stretched. I mean, the panels slipped down about 1 inch during that time.

In practice, there isn't any wrinkling, or horrible distortion, nor buzzing sounds. Sounds mostly ok. Maybe loud choral passages sound a little distorted, but I am not sure if that is due to the recording or amp either.

What is the default tension supposed to be on these panels anyway?
Will the hairdryer trick work for something like this? Or should I just leave things alone?

Your description of tension sounds normal. But over time the adhesives will tend to let go, so keep up the clamping force to keep the ESL sandwich from separating (and keep them from slipping down).