This car hasn't been run much in the last two years -- the PO left it sitting for at least that long. I have noted a lot of crusty, oily muck on the engine block, in the engine compartment and front suspension, most noticeably on the passenger (right) side of the engine bay. So it appears as if the engine has been blowing/leaking oil for some time.

When I pulled the plugs, they were pretty black and sooty, although it struck me that it was attributable to a long-term running rich condition, rather than to fouling due to oil blowing past the rings.

I'll try a wet compression test as you've suggested, and see if the compression figures change.