My new MBP 13" often dips into the 4GB+ RAM used range running OS X 10.8.2, more than I regularly saw with an older 2008 model that only had 4GB running Lion. Granted, some of it's just "wired" but "inactive" (ie OS X will reassign it when needed, but for the time being, is letting it stayed loaded with what was using it previously). I picked up 16GB from OWC for $95 (always used OWC RAM in my Macs, never had a problem).
That said, pops/crackles are often CPU-related. You can try making the audio buffer higher/larger, that will lower CPU strain a lot.