None of the cars were stored properly. Some may be worth restoring, but they could have been worth dramatically more had the owner been an enthusiast.
For instance, the open exhaust pipes on the old cars (this was before cats) will allow air/moisture in through the open exhaust valves...which is not a great idea for a cast iron block, or iron valves, or for iron pistons.
Obviously the cars had no dust covers or rodent blocks/traps, nor even suspensions supported (e.g. on blocks).
From the above alone I'd guess that the poor owner left the old brake fluid in to harden in the brake lines (bye, bye) and clutch lines...and the old motor oil was probably left in to acidize, too.
From all the dust, it's pretty dry in there, no surface rust , and the tires are still inflated other than the one without wheels. They're in no worse shape than your typical "garage find" with an elderly person who stopped driving. We're talking fifteen years here. The building walls are concrete block, so nothing to attract rodents that I can see. I'd say quite a few of them have significant value above and beyond salvage.
Wow, thanks for your comments. Makes me realize how badly the previous owner bungled his preservation efforts, if indeed, he was even trying. It makes me think that it may turn out that he was nothing more than a prolific car thief.