Good or Bad idea?? ??

I think the consensus is that you may have some issues with the suspension drying out. You should probably factor in the cost of a rebuild, unless the maker tells you otherwise.

Depending on storage technique, there can also be corrosion issues. I have seen aluminum cantilevers that have corroded over time due to being stored in a humid climate. The copper wires of the generator and the suspension wires can also corrode if not stored in a dry climate. Suspension rubbers drying out is another problem. That can happen even if the cartridge is stored in a dry climate.

canteliver can fall right out if it is too old

I would pass

As Swampie says, you should factor in the cost of rebuiding the cartridge unless it is much less than ten years old and stored properly. Use should also be factored as well as the price of said cartridge. I believe a rebuild is around 1200.00 for Koetsu.