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
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!
guitared---Barry Diament, the guy I heard about the roller bearings from, put his Magneplanar 3.7's on them, and uses slightly inflated bike tires between BB plywood planks for his electronics, even in his professional recording studio. Almost as good as the Seismic Pods, and a lot cheaper!
Hi BDP, I've done exactly that with each of my components and could not believe the improvement they made.  I'm using marble tiles instead of plywood, it was actually cheaper!  I also have marble tiles under the speakers and above the homemade rollers presently, and every aspect of the sound has been improved over just spikes on the hardwood.  I'm a little unsure about adding the inner tube under the speakers for stability reasons; the system is in a living room and I'm worried someone (or some dog) will knock them over.  

Has anyone tried this with a more traditional floor standing speaker?  I may get 2 more tiles and try sandwiching the tube or rollers between them.  The cabinets are rectangular so I need the tiles to allow placement of the rollers in an equilateral triangle.
I'm anti spike for speakers since putting Vibrapods under my Silverlines. Keeps them independent of floor vibes and they simply sound better than they did with spikes.