Hmmm... This is an interesting topic that's morphed into, well, a different interesting topic.
I have always distrusted sensitivity ratings. I guess the main reason it that the measurement is at 1K, and I'm not sure that tells me much of anything about a speaker's performance. (Same with Ohmage ratings, because resistance is anything but flat across the frequency spectrum.) At best these are clumsy devices that probably mislead consumers more than they help. Because I have had magnepans for the past nearly 40 years, I've simply tended towards amps with enough juice to drive them. One key reason is that most of the gear I've seen destroyed has resulted from folks clipping their amps - a fairly obvious reason why inflating sensitivity ratings is not a good thing.
Vibration damping and plasticlay is one of my all time favourite topics. Frank is, of course, the guru of plasticlay. Some 30 years ago he wrote it up in Audio Basics, I tried it, and he was kind enough to reprint my letter to him extolling its benefits in a later AB issue. (Remember when we wrote letters?) In that case it was my fully damped turntable (and yes, the stuff is great for wooden box-style TTs).
One of my subsequent speaker purchases was the biro L/1 that Frank distributed for Mithat Konar, and my uderstanding (Frank can please correct me if I'm wrong) is that Mithat applied the same principles of internal damping. As Frank predicted, I regret selling them 4-5 years back.
When my Tympani 1(U)s gave up the ghost 3 years ago, and my spousal unit insisted that I rebuild them instead of junking them (so much for WAF), it gave me a chance to try out approaches to damping the particleboard. (In the tympanis, pretty much everything vibrates and makes "music" or something vaguely similar.) I used silicone caulk in the corners and at the join between the elements and the particleboard, and plasticlay over the rear surfaces. While it obviously couldn't solve the fatal flaws of the tympanis, the improvements were quite noticeable and for the better.
My current mains are VMPS RM30Ms. In these, Brian Cheney uses mortite to tune the passive radiators. The mortite is, technically speaking, on the outside of the enclosure, and well away from anything electrical. So I think the issue Dennis raised is probably moot. But it (1) is very useful and audible, because in this case its use is actually integrated into the design and (2) sticks really well (which is a potential problem with plasticlay). IIRC Brian uses something to damp cabinet innards, and sells BH5 as an upgrade. In the spirit of overkill, he's taken to building cabinets for his subs using 2" MDF.
So, Dennis, all I can do is encourage your experiments and let you know that I'll be really interested in following your results.