Moin,

when it still holds "Elaboration isn't wasted on this hillbilly, ... " here is a remark on gravity:

In an ideal approach it has no effect. Regarding the suspended cone as a spring, force and elongation are proportional (linear behaviour). This means that for a certain force there is a certain elongation. This is even true if there is already another force acting. When turning the cone facing upwards, there is the force of the cones weight, but the proportionality will not change.

Facing upwards the null position will change. It depends on the manufactorers recommendation whether a speaker may be used in this manner. A very high compliance driver may run into complications but there could be added a small amount of DC (I have never read about such an approach, but it might work because at full power the currents and forces are much bigger.)

"I mean, I know that the old 'equal but opposing force' rule applies to a 30g cone and a 30 lb basket, but at mW levels, it's hard to imagine any more than a shorthair on a gnat's ass."
Newtons law is always true. But for example when looking into atoms you need quantum physics as well , looking to the stars you need theorie of relativity as well. Resonances can be a real pain. (Once I rolled a speaker with a heavy top over an uneven ground. The top, ca. 30 kg, jumped down like a ball .)

"Then there's the infinite baffle...that isn't...anymore than an infinite horn is."
Yes, these are only theoretical simplifications to get a start. Electroacoustic is not that easy (- except we are "esoteric" and have our one and only golden rule - ) although with todays standards we can easily be very successful . When turning into a practical design we always have to make a compromise, or at least we have to consider new effects or rules. We can approach the infinite baffle by a closed box. But all of sudden we have resonances as well, and the mass of the moving air will change too.
When tuning a closed box it is often done by changing the stuffing. A better way would be to choose another volume (rebuilding), as the fiber filling has ist own laws: "Fillings" by W. M. Leach, Jr.
http://users.ece.gatech.edu/~mleach/papers/Filling.pdf

Hope this has been useful.
___________
Peter