Idk, 19,99€ seems fair to me. If they charged another 50€ for this I would agree.
If the 900/1000 is worth the extra money also depends on the realism you want. For example Lufthansa doesn’t operate the -700 anymore but only the -900. So if you want a realistic Lufthansa flight then you need the -900.
If you don’t care about that then maybe you don’t need it, however nobody should complain about a small number of differences, that’s just how it is in reality.
I personally love the CRJ-900 and I never touched the 550/700 again since it was released.