I like overkill.
Yeah, I have that problem too! I'm not buying small PCs here and there all the time for individual jobs so when I do buy a new one I like to get something that's in the upper half of the current state of play so that it lasts a long time.
That spec of machine will be a very good media server I think, nothing wrong with it at all. You could probably do a few video conversions at the same time as well! I know that the CAPS machines have "audiophile" bits in to suppress electrical noise and to avoid unnecessary CPU work etc, I don't know how far down that route you want to go but it's something that I've not been too bothered about, I just wanted a fast and silent machine.
My Intense PC, which is dedicated to MC (both audio and video) has the mobile i7 as detailed previously, 128GB Crucial SSD (SATA), Windows 7 Pro 64, 16GB fast Crucial RAM (2x8GB), media files stored on a NAS, audio coming out of either the onboard Intel SPDIF or via a Soundblaster USB sound card - still playing around with this - and audio for video is bitstreamed via HDMI. It's small and cute, looks like a router! I've taken the wifi card out as I don't need it. It boots into MC in about 15 seconds and wakes up from sleep (via JRemote) instantly, but MC will hang for a bit while the NAS drives spin up after sleeping.