USB 3.0 is still limited by the hard drive in the enclosure, which if it's not an SSD (or RAID 0, but still) it will bottleneck. After Effects will benefit more from all that RAM though but only from a RAM Preview point of view (mostly, unless you have some really crazy comps)? You'll be able to preview more frames (and larger frame sizes)? This is only good for seeing how a small section of the video looks. While you are scrubbing the timeline, in Premiere and AE, the source is being pulled from the hard drive, not from RAM, so the bottle neck will be there.
Don't get me wrong, having all that extra RAM is handy when you want to render a preview in AE so it's not too much of a waste but I think from a performance point of view, you should've spent your money on a larger SSD.




