Sorry for the long wait on reply, went away over school holidays!
Basically I looked at a bunch of options then decided to build a mini server. The main issue/problem/challenge is that I wanted to use my 27" iMac as the screen (toggling between the mac and server) rather than go back to using my 24" Samsung 1900x1200, which now looks fairly average compared to the iMac screen, which is glorious. My iMac only has thunderbolt, not display port so I need to use a thunderbolt motherboard. Also the Server needs to be small (to get partner approval) and due to space constraints.
I ended up getting a Gigabyte GA-Z77MX-D3H TH off ebay cheap. Then bought a 3770K, 32GB of 2133 Kingston Beast ram, a Noctua 12U Slim (agonised over water-cooling but I need it to be silent or as quiet as possible), and a bitfenix Prodigy M in White. My Samsung 500GB SSD, velociraptor, 2 WD Blacks will go into this. I'm still putting it together, but it will be a quarter to size of my original rig and fits in (being white). I agonised over this - I couldnt find (to purchase) a Z87 Thunderbolt motherboard in M-ATX.
This probably seems stupid given 1155 is done with, but I really wanted a small machine for the partner approval factor and to use the iMac screen. I dont think I'll notice the difference to a 4770k and hope the faster ram and SSD and a decent overclock will make up for it. Also the MB comes with Virtu, so when I get a new GPU I hope it will work to output the discrete GPU signal via the Virtu s/w thru the thunderbolt cable. Its been done before but of course who knows if it will work in the end. The idea is that 99% of the time the server will run VM's I need because of my job, and Windows software I would rather run native than under VMWare on the mac and act as a media server (my NAS experience has put me off NAS's for now). Then when Star Citizen comes out, I will use it to game. I now just need to find a good GPU to run at 2560x1440.
Maybe when Haswell v2 comes out, someone will bring out a M-ATX motherboard with TB, PCI-E SATA, DDR4, etc and I might refresh it all again. I am finding that with ebay I can get a large percentage of my money back and tax deductions/depreciation covers the rest.
Ideally I might have moved house by then and I can go back to a full or mid tower, and Haswell-E .... or if I can afford it a E5 Xeon.
My strategy with my old Core 2 rig was the same as yours, constant small upgrades. I think though now that I'm a bit more cashed up, I'll buy the machine I need now and then upgrade in 14-16 months again. Maybe hand down the current rig to someone in the family.