I think the main issue with the argument that silver should be much, much higher in cost because most investment is in paper and not backed by physical silver falls apart when we look at silver as a commodity. If it even moves up into the $100 range it can be replaced by other products in many cases.
If it ever becomes sought after as a store of value like gold that argument could change but for now silver has a cap unless there is another entity that tries to corner the market. In that case there may be an artificial spike but a speculator in silver would want to hold their silver as a tradable entity as the market could move very quickly up and back down again as we've seen this week with GME and other stocks.