The difference between the EMI Racing camber plates and the DP Racing camber plates is in the materials used - the design is identical. The EMI Pates are an upgrade (actually made by DP Racing for EMI) using 7075 aluminum, NHBB Astro COM10 spherical bearings, 316 stainless Torrington bearings, hardened spring steel bearing washers, 316 stainless bolts, etc. I ran a set on my 240Z for 10 years without having to replace anything, sold them to a fellow racer, and he ran them for another 5 years before he sold the car to another racer. As far as I know they are still going strong somewhere in the midwest.
The DP Racing plates have also lasted a long time although I don't have any specific numbers from my own usage. I'm sure other folks on here can chime in with their experiences.