I haven't ttied anything like the ones you mentioned, other than the spike. I have tweaked the subwoofer distance (almost doubled the actual distance) and noticed the bass was a bit more responsive, less sluggish.
I have a velodyne DD-15 and puchased a symposium svelt shelf to put underneath.I replaced the rubber footers with the svelt so the bottom of the whole sub cabinet rests on the svelt.What a difference without trying to listen.Clean bass just popped right out,almost as good as no sub cabinet,I guess you could say that most of the bass was freed up from from the physical part of the cabinet.So i replaced the spikes on my revels(50-as)with the svelts,For me I won't go back to spikes or rubber feet.I like upgrades or tweaks that you don't have to try to listen,They make you listen,I like surpizes like that,Hope that helps(it does for me).
I've had excellent experiences with Star Sound's Audio Points on my custom racking systems. In fact, not too long ago, I became a dealer for them.
You might also try experimenting with ics for your sub. All ics generate time smear to either a very small or great degree which leads to ill-defined and sloppy bass (and other things for main speakers). My limited experience tells me the vast majority of scs and ics generate great degrees of time smear and you'll never know it until you try one with less time smear.
Audience (AU24, Maestro, and Conductor series) or Audio Tekne are two names that come to mind that generate an absolute min. amount of time smear. Speltz Anit-ICs is another.
Properly addressing vibration mgmt techniques along with installing good quality ics can make the sloppiest of subs sound extremely tight, deep, fast, and well-defined. Which is what true bass is supposed to sound like.
I too noticed an improvement when I placed three medium-sized cones under the sub. The cones were resting on a piece of granite block. Slow plodding bass was gone and the speed and definition were significantly improved.
This was compared to the sub directly on a carpet floor.
I was surprised you can support the sub with "a pair" of brass spikes? I thought we need a minimum of three?