I've never found any single build that is "it does it all perfectly". I'm currently using an i7-2600K+6770, 16GB RAM, and store everything against a 22TB WHS.
Why you chose the components you do matters a lot in comparison to what you are trying to do. My WMC is primarily a WMC. However, I find that while I store a lot of BDs in full MKV (uncompressed) there are times I want to recompress a BD, because it's something I may not watch as often. The difference between the time it takes for me to do that on a 2600K vs. doing it on a I3 is significant.
My MCE handles 2 Ceton Tuners. I can easily, with no hiccups, re-compress a BD in the background while I'm recording several shows. I don't worry about disc stumbles, etc.
Those things wouldn't be possible on a G530, etc.
The best advice anyone can give you is this (and I've said this repeatedly) find out how much money you want to spend, and then get the best combination of components you can reasonably afford. Take a lot of factors into consideration: what you'll do with it, what kind of video quality you expect from it, and what you'll ask of it on a routine basis.
The question about "more then 4GB of RAM doesn't matter" is bogus. Each of my MCE extenders grab about a gig of memory. x264 encoder will grab as much as I want to throw at it, and the more I have the less disc thrashing I've got.. etc. RAM right now is crazy cheap. 16GB ran me $70 at Microcenter. So, why not? I stocked up on HDDs before they went through the roof and people said "why buy all those 2TB" yeah, sure paid off now, didn't it? Those 2TB I bought last summer at $71 seems like a crazy good deal now
So, it depends on what tasks you have in mind. If you're sporting a plan of extenders + more then six tuners, the more "oomph" you have helps. Plan on recoding titles? Helps. Hell, even the time if you automate MCTVConverter to manage your DVR recordings..
You can shoot the moon and spend to the ceiling, or you can grab at the floor and spend cheap. And there are a lot of benefits in both strategies. Nothing is really wrong with a G530 or an i3 build; lots of people love it.
It's the same reason why some people will buy an Oppo bluray player vs. a $130 Sony BD player. They both play BDs. Once just costs more.. for certain benefits. So, you always have to ask if the juice is worth the squeeze