We just used a spare under our Ford 250 while repairing one of the tires, and the undermount was a bear. Our RV spare is mounted on the back, but still was difficult to remove after sitting there immobile for 10 years or so.
I think an older spare is just not that big of a risk, but then again I take risks other would not. You never know when you will need a lot of things, but we have roadside service and probably would replace our tire before we used the spare very long. It is truly just an emergency measure. YRMV as they say.
Then again what is another $250 when you are out spending money right?