Should I build plinths or screw spikes into cabinet?


I've got a great old pair of B&W DM640 floor standers, but I don't have the plinth and spike kit that were sold as an option back in the '90s.  Since I have been unable to track down a kit online or directly through B&W I am planning on building my own.

The speakers themselves were built without any isolation system on the base of the cabinet, and were set on top of adjustable "lugs" which were incorporated into the top of the optional wooden plinths.  Each plinth had four basic spikes mounted at the corners.  This sounds easy enough to replicate.

Does it make more sense to simply drill into the base of the cabinet and mount the spikes directly?  The tweeters are nearly at ear level, so I don't need to lift them much.  I am a little hesitant to make any permanent alteration to the speakers, however.  Any opinions or alternatives are welcomed!
guitared
Good luck Guitared, I'm sure you'll come up with something for your speakers that's cost effective. I have little experience outside of the spikes I was provided with my speakers, but your post brings up an interesting quandary. Couple to the floor with spikes or decouple from the floor via the Townsend or some other method as suggested by Infection & bdp24. I imagine that's been debated endlessly here and elsewhere.....
As your budget is ideally less than  $100 then obviously the Seismic Bars are out of the question! 

Perhaps you could fashion your own version...!
A DIY version of the Seismic Bars could be a pair of Baltic Birch plywood shelves separated by a very slightly inflated bicycle tire in between them. With a trio of roller bearings between the speaker and top shelf you will have excellent isolation without the non-linear filtering caused by "lossy" materials (rubber of any type). 
I've added spikes into threaded inserts, but I've also ordered DIY roller bearing setups.  The latter will likely end up being used to isolate my components since I'd prefer to reduce the risk of a loudspeaker getting toppled over (baby on the way!), but I plan on tinkering with both.  Thanks again everyone for the feedback!
After getting the speakers up on the spikes I had a quite significant drop in sound quality, particularly in the low-end.  I have suspended hardwood floors, and it turns out I'm suffering the same side-effects from coupling seen by many others.  I should have done more research...

I've got them up on ball bearings in furniture floor cups now (spikes removed), and I am hearing a great improvement.  I'm going to throw some stone tiles between the bearings and the spikes soon, then probably bump up to some vibrapods or feet/isolated spike cups from Herbie's audio labs.

Infection, I wish I would have investigated the Townshend website further instead of just joking about the price of the seismic bars!  They have a great video that explains the benefits of isolation vs. coupling, and I would have initially gone in a very different direction!