While these sort of coins are legal tender, that is not the reason that I acquire them.
I buy them since I like the design.
I had a laugh reading on another forum about the folks who "over bought" the Canadian 20 for 20 coins and now are moaning about the hoops they need to go thru to get their money back.
To me the only time it make sense to buy more than what you need for your collection, is when you are doing so to help others out.