They are not investments, just depreciating assets. Ask your accountant!
Streaming will overcome.
This.
However if you like them, collect them, but understand there is already replacements for blu ray being worked on. I believe its Hitatchi (I could be wrong) that has optical media capable of storing 300 gb at the moment.
That being said the read speed needs to be as fast as Blu Ray, devices need to be able to process the amount of data at the same speed, etc etc. There is a lot of variables in the process so its not like a replacement is right around the corner.