Not terribly much, unfortunately. It's a middling system, not particularly impressive in any spec, with a built-in power-hog CRT. The monitor-less Quadra 605 is a heck of a collectors item; but this is just a monstrosity.
It's not a horrible machine for the time, nor even particularly bad now; it's just fairly common as well as large.
I'd estimate it would be worth, at most, $50. Maybe at some point ridiculously far in the future, if you keep it in absolute pristine condition, fully functional (means replacing capacitors at some point,) it might be worth a lot; but we're talking a long ways off, when CRTs are seen as curious antiques, and 68k Macs are as rare as hens' teeth.