The bar collecting market is small but somewhat fanatical according to my LCS. Some bars are quite rare and fetch 10x spot or more. So keep an eye out for older/ unusual size bars.
That's not my collecting area, which is mostly one ounce rounds, but I would not turn down the opportunity to handle a nice chunk of silver. Once one of our LCS had a 1000 ounce bar they were selling. I assume that someone bought it eventually.