i thought of that too but nah.. too much effort..
You're proposing to replace a motherboard and processor, and maybe a power supply, in a computer. So, how would using one of the other cases you have be too much effort? Can you not make to effort to remove and/or install a few other components if necessary?
I have 3 amd cases And i have 3 intel cases.. each case has parts of somekind but theyre too old and im in no mood to keep up with a slug pc.
If you put new or newer components in one of those old cases, then it wouldn't be a "slug pc", would it?