Spiking speakers not designed for spikes?

Millercarbon is a smart human.  Back in the 80s, we did exactly that with solid machined aluminum cones under floor standers.  The effect was immediate.  We used a 3 cone system for each side.

Another possible upgrade is simple crossover and wiring work.  Keep same values of caps and find some decent Solens or better.  Almost any decent speaker cable wired in is an improvement over stock wiring.

wooden bases that I’m nervous about removing or drilling into.

Use "T" -nuts of the same thread as your spikes, and for good measure coat the outside of the "T" nut with liquid nails before you hammer them in, and you’ll be fine I’m sure.

https://images-na.ssl-images-amazon.com/images/I/81x9eKE2eAL._SX425_.jpg

https://images.homedepot-static.com/productImages/5954888a-159c-46b2-a760-a79dcc9a1c21/svn/liquid-na...

But remember, spiking a speaker into suspended floor is a no-no as the floor becomes a sound board for the bass destroying any tightness to it. They should be de-coupled not coupled on this type of floor.
Only spike a speaker into a solid cement slab floor that can't act as a sound board. 

Cheers George

what doe's 'spiking' mean?

Though solid cement floors are less resonant than are suspended wood ones, they are still plagued by seismic vibrations. Spiking is so 20th Century ;-).

@bdp24 do you have a suggestion for an alternative to spiking?
@georgehifi Thank you!  I had a local guy suggest those same nuts.  Will it be simple to find the right threaded spikes for those?
@celtic66 How big is the payoff for the crossover upgrades?  I've opened up these suckers a couple times, and it's a pain in the ass to get them back together due to these expanding rubber nuts on the back of the drivers.