Anyone able to help with this question?
I have only 3 GB myself.
I have seen up to 4 instances of AE when rendering out, though.
I have only 12 GB. There is however a sound reason for that amount and not 24 or even more. A PC is only as good as it's weakest link. Usually that are the mechanical parts, meaning disks. And there is always a budget limitation. And there is availability of parts.
With all these restrictions, only 6 DIMM slots, and the limited choice of DDR3-10600 sticks in anything other than 2 GB sticks (just looking today I was not able to find any 4 GB sticks, apart from Kingston Value RAM in ECC edition with CL9 at triple the price of 2 GB), I considered it better to invest in disks than a long search for very expensive memory sticks.
These considerations make that the most logical amount of memory today is 12 GB and not 24 or more, at least on mobo's with only 6 DIMM slots.
Would Adobe use more than 12 GB, even up to xx GB, well I don't know, but the diminishing returns of the extra memory at very high prices make it more logical and economical to invest in a good disk setup.