I would recommend Intel processors over AMD for Adobe products.
Does Hyper Threading affect the way AE / Premiere render?
I can't talk for Premiere. For AE, it's perhaps marginal compared to the number of physical cores. And could be in some cases counter-productive if it tricks AE's multiprocessing system into believing there are twice as many cores, because of the way AE assigns RAM to the rendering instances it launches for each core (when "Render Multiple Frames Simultaneously" is enabled in Preferences).
Will I notice a difference in speed from 8GB to 12/24GB for memory (for AE / Pr)?
Yes, 8 GB is actually the absolute minimum you want for a quad core system (2 GB per core).
After that, it depends on the content. For HD sized Comps, large source files and/or 32 bpc processing, having more RAM would lead to better performance and reliability.
I would also like any suggestions on graphics cards (FireGL vs Quadro or GTX vs Radeon) to boost performance. I'm not much of a gamer and I would like to concentrate more of power on production.
In AE, OpenGL previews are meant to provide a smoother/more responsive experience when interacting with the application. It won't help with render times in most cases. A medium to high end consumer level card should be fine. No need to sell the house for one of the pro level models. Keep an eye to the list of officially supported card/driver combinations.
Thanks for your suggestions. Sounds like a solid choice to choose Intel - as long as the memory is there.
I also appreciate your help in furthering my understandings of how AE computes with HT and multi-cores.