I see that you put Hitachi SATA drives in your servers. While they are great drives for workstations, they don't offer very optimised performances for server access patterns, at least according to SR's benchmarks. The two fastest 7.2Krpm, SATA drives for servers are the Western Digital (which I won't suggest) and the Maxtor MaxLine series. And this
store list the new 500GB MaxLine Pro at 338$ each. This
other place sells the 500GB Maxtor DiamondMax 11 at 335$ too.
And just in case you would like to get rid of a few servers, there is this
3U chassis with a triple redundant 760W PSU that is on sale for
841$ (free shipping). Add a
Supermicro H8DCE (
348$), which have 8 SATA 3Gbps ports integrated, plus two of the 3Ware 8506-4LP that you already have and...you could end up with newly found closet space
. Just wait a month before buying dual-core s940 Opteron. The 270 for instance, which currently cost 845$, will drop to around 480$ after the announced mid-February price cut. And the 4 3500rpm 92mm fans into the Supermicro are probably too noisy. Nothing forbids you to replace them with 92mm Panaflo fans. The drives won't produce that much heat anyway. As for reliability of the entire system, the PSU is triple redundant and all the parts are industrial-grade, so the whole thing is probably safer than what you currently have. And you would make savings on your electrical bill.
Of course, filling up the 15 bays with 500GB drives, plus the chassis/CPU/2GB RAM will cost you slightly more than 7000$, but hey, that's your part to figure out.