Going off the local PC only idea, you could script just your rebuilds of them in the off chance something goes south, along with maybe a disk image with the majority of common games loaded. This is just thinking along the lines it's friends and family, not the general public. I'd probably use gigabit Internet (or more) which makes updates you're missing fast, while Steam lets PCs on a LAN share updated files and save bandwidth.
Did you consider patch panels or things like PatchBox to organize those UTP cables or allow for changes in your switching later?
The way I have it set up, I am essentially maintaining only one PC, in a totally normal way. I update Windows by pulling up Windows Update in the control panel, etc. Since I only have to do it for one machine this is fine -- orchestrating updating 20 machines sounds like a pain. Yeah I know there are enterprise tools for this but why bother?
Once I've updated that one machine I just run one command on the server and now all the machines have cloned it. At the end of the party I run one command and all the machines are reverted.
Also I can give everyone full admin access to their machine (which you sometimes need for games) and not have to worry about it, because I know it'll all be completely reverted later.
But to me it sounds harder to maintain than just wake on lan + pxe to reimage the machines before every lan party.
I think it's specifically the fact that they access their disk remotely live that's bothering me.
Why not just image it to the ssd and call it a day ?
Well, OK, admittedly in the latest build, I have some stability issues right after boot. But in the worst case the machine reboots once or twice, and then it works. If it doesn't BSOD in the first five minutes then it's good, and everything works every bit as well as if the storage were local.
Whereas reimaging all the machines would actually take more time than waiting for this stability issue to work itself out. And would also require that I install storage in all the machines big enough to hold the main image (currently, they don't have this).
Overall I find it more convenient this way.
Note that the stability issue is specific to my hardware/drivers -- I didn't have any such problem in the Palo Alto house.