Have you ever considered investing in collectible guitars? Some of them sell for pretty substantial amounts.
For example, Heritage Auctions recently held an auction of entertainment memorabilia, with a lot of interesting items that were put up for sale.
A guitar that Bob Dylan personally owned, a Fender Electric XII Twelve-String electric guitar was hammered at $187,000, including buyers premium. This was the guitar that Bob Dylan played on the Blonde on Blonde sessions.