Tightening loudspeakers screws...

My advice is to tighten the screws just to the point of firm resistance. I have owned several Meadowlark Audio speakers that also had a dampening material between the drivers and the baffle. I simply stop turning the screwdriver when the screw tells me to.
Don't leave the screws loose but don't over tighten either.

I believe the logic of leaving the screws loose is to convert vibrational energy to heat by having friction between the driver flange and baffle. It's a bit of a stretch...

I believe the foam under the driver is to achieve an air seal. Silicone caulk works even better, and holds the driver in place without need for any screws at all. If it becomes necessary to remove the drive this is not too difficult to do using a razor blade.

Here's an interesting video about tightening loudspeaker screws and changing to brass screws. Starring Rick Schultz of Virtual Dynamics.
http://virtualdynamics.ca/the-oddiophile-eps--1/

His reasoning for using brass screws is pure bs. Then again, what do you expect from guys selling the acoustic system resonators?