Putting up a 100+ million point game on SM is no where near as exciting for me as a game where I was fighting and working my way through Jericho on IM. If you want a rush and excitement that few games deliver in pinball get IM. If you want to be a better player get IM. No competition between the two on those topics mentioned above.

Edit- if you own SM and ST move one of them out of your collection for another pin. Shots are to similar. I was thinking of trading my ST for a SM last week, but changed my mind because the shots were so similar to me. I would move SM first over ST. I own ACDC also and IM, ACDC and ST work perfectly for me for Stern titles, but you own MET also, so that brings another dimension. If you like ACDC and MET then get IM. If you like TSPP, LOTR and POTC get SM. Good luck!