I am sure that the training course is an excellent investment in time, for those with enough time to spare to enjoy it. For me, it is never about the coolest gun at the range. If you are paying $500 or more for a weapon, it should be considered an investment. Owning a desirable gun inherently makes it more valuable. It is the same with a car, or house, or land. If you spend a little more money up front, you may see a dividend on the back side. I have made made some good investment decisions and some bad ones. Trouble is, you never know up front which way it is going to be.
I would not look at firearms as an investment, UNLESS you're talking about some sort of rare ones, machineguns, or extremely old and/or collectable firearms (say 100+y/o fine side by sides for example). The MR556 is never going to fetch more money than it is currently going for. There's nothing particularly special about it to achieve some sort of rare status, and production was not extremely limited. Maybe it might maintain it's value, but it is not going to appreciate, I can pretty much guarantee you that. Personally, I look at these as bullet launchers for killing stuff, and that they should be treated accordingly. I might feel differently if we were talking about a 110yr old side by side.