I just spent $500 extra on the home cluster in one fell swoop.

$500+ dollars for memory for two of my hosts:
Refurbished: Micron 48GB (6x 8GB) PC3L-10600R ECC Registered DDR3 1333MHz Server Memory Kit for Dell PowerEdge R610 R620 R710 R720 R810 R820 R910, (6x Model MT36KSZF1G72PZ-1G4) - Newegg.com
But now the cluster will have 168 GB's of RAM across 4 hosts w/ the 8 x E5520 processors.

Next month is a good number of Velocoraptor 10k drives and 4 SSD's to make a vSAN across the hosts and either a FCoE or FC network just for vSAN storage.

I may just make a Tier 1, 2 and 3 Storage fabric for the home-cluster between vSAN and the two other NAS's since one is a RAID 5 and the other is a RAID 10.