It doesn't sound like there's any critical issues involved in going with solid mounts... other than a somewhat compromised ride quality. Since the old bushings were completely shot and were riding metal on metal and my shot engine mounts had the engine bracket resting on the subframe, it probably wouldn't be any worse that it was.

Since my choice is likely subframe spacers or solid bushings, I may just give it a try and report back. (I'm planning on doing an engine swap and will very likely need some additional engine-hood clearance. May be able to notch the subframe and keep the stock bushings... but won't know until I do a trial fit.)