Last year, I worked on getting my mobile data usage down and part of that was turning off background processes. What I found is that battery life goes up considerably by turning off almost all of the background processes. The downside of turning off background processes is that there may be a pause when you open an App as it will need to load data.
In general, I think that I prefer to leave the background processes off and get the better battery life and the lower mobile data usage.
I agree on dual-core (or two threads) being enough for phones and tablets. I don't do video editing or other multithreaded applications on my mobile devices (even though such software exists). I find it far more efficient to use one of my Core i7 systems for video transcoding or audio editing. I can't realistically think that we'll see i7 performance and memory sizes in mobile devices anytime soon.
Yes, it's nice to have a quad-core Snapdragon whatever in my wife's phone but I don't think that it really makes a difference over dual-core given that the most CPU-intensive thing she does is watch YouTube videos on it.
Also, most of the academics that I know (working in industry now) do know that user apps are generally not well-suited for many core/thread systems over single-threaded. Server applications do often run very well on many core/thread systems though.
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