What's wrong with 640K? You can do plenty with that amount of RAM; I've personally spent more than a decade of my life working on machines with that much RAM or less.
My first computer was an Apple ][ in 1978 and the big choice was between 4k or 16k RAM. That's Kilobytes. I got the 16k version, which was a stretch financially, but you needed that much to load floating point BASIC (from cassette tape - they hadn't inroduced a floppy drive yet). Otherwise you were limited to the integer BASIC burned into ROM. 48KB was the maximum RAM you could put in the original Apple ][.
In the 80's I had an AT&T 3B/1 "Unix PC" which I thought was so cool… real unix (although Sys V) on my desktop! It had a 68010 CPU and 2MB RAM. Got very slow when it started swapping, I think the hard drive was 40mb. It took a lot of 5" floppy disks to back it up, LOL.
Got an i5 MBA with 4gb RAM in 2011 (the max available) and it ran all my software (Final Cut Pro, Strata 3d CX, Vue Infinite) twice as fast as my 2008 15" MBP. It was probably swapping but I didn't even realize because of the SSD. Now have a 2013 i7 MBA with 8gb (again, the max) and it's a little faster but things feel pretty similar.
My software is getting old and most of it can only use 4gb RAM, so I'm completely happy with my quad i7 16gb Mini. I think it will also be fine for the next year or two when I move to newer versions of 3d and video software. Nothing wrong with having a Mini that could accept 32gb but seriously, we know that isn't going to happen, right? And if it did, you would have to buy the 32gb model at some outrageous price directly from Apple since the RAM would be soldered.
Sorry, I lost interest in games with SimCity, back around 1993. It ran great on my Mac IIcx! Have Macs ever been competitve as gaming machines?