You must not overlook the fact that below FL290, the standard separation was 1,000 ft. even
prior to introducing RVSM. Barometric Altimeters and older types of Air Data Computers are/were less accurate at higher altitudes. FL290 was selected as a suitable change-over point to increase vertical separation to 2,000 ft. to allow for this reduced accuracy. With the use of digital technology and better materials technology in pressure sensing devices, altimetry equipment became sufficiently accurate to allow 1,000 ft. separation to be applied above FL290 - provided particular aircraft and equipment combinations were proved and certified to have necessary system accuracy.
Eurocontrol published an excellent bulletin on the use of Collision Avoidance Systems and this is now being circulated around the airlines. If you haven't seen a copy, you can get it
here. The document illustrates the issue much better than criticism of implementing both ACAS and TCAS in the same airspace.
In short, the key to successful collision avoidance isn't a function of altitude separation. Its a matter of
Follow the RA to maintain safe separation and avoid collisions.