There has been a plethora of threads about saddle materials over on AGF. The collective wisdom is that the "best" saddle material is very guitar dependent.
Bone, elephant ivory, WA Elephant Ivory, Fossilized Walrus Ivory, Tusq, Micarta, Corian, etc. can all result in subtle or not-so-subtle tone differences depending upon the guitar; shape, top wood, and body woods. There are some AGF members who assumed that changing from the manufacturer-supplied Tusq or Micarta to bone or some other "natural" material would be a no-brainer upgrade, only to find out that the guitar actually sounded better with the original saddle material.
I would not assume that changing all of your guitars over to WA Elephant Ivory will be an improvement for each one.
First, I would make sure that all of the existing saddles are flat on the bottom and fit properly in the saddle slot. Then you know you have a correct baseline for comparison. Also, aural memory is very poor for most folks. I think you really need to record identical sound clips to evaluate different saddle materials. We sometimes hear what we want to or think we should hear. Especially if we have spent a lot of money for the supposed upgrade.
If you have a specific tone adjustment in mind, such as an overall brighter sound, or better string-to-string balance on a specific guitar, then the info on Bob's website about different saddle materials is typically spot on. I've switched from Tusq to EI for a more mellow and balanced sound, and from Bone to FWI for a slightly brighter tone on two different guitars, and the results were great. I also had a guitar for which changing from Tusq to bone was not an improvement, so I stayed with the Tusq. I think a sweeping change for the sake of change is risky.
Remember also that changing the nut material only effects open strings. If a string is fretted, the nut material has essentially no effect.