The main thing you get with the signature ESPs is quality.
I have 3 GL signatures,(Kami prototype, Kami 2 and a 91 GL smakes & Skukks with strat headstock & side dot markers).
I have other guitars from Gibson( les Paul custon), Ibanez (artist and Presteige) and PRS ( 1988 24 standard) , and there is a very noticable difference, even with these high end guitars, is just how much better built, and just how good by comparison the ESPs feel.
I played an Ibanez RG presteige model( now sold), and it felt like bolsa wood put together in a shed by comparison to the ESPs.. Theres simply nothing I could fault with them. BTW, the snakes and skulls feels totally different to the Kamis, but they can sound similar. - They are the best guitars I have played, and i have played em all...