Right. You could, however, play In-Betweener w/gem and play another immobile object.

Not really a shame at all, in my opinion. One, it keeps the game balanced. Two, thematically it makes no sense to have two or more of any particular Infinity Gem... they are singularly unique in the Marvel universe.

It makes as much sense as having two Supermans.

All the various Crisis stories and what-not would disagree.

Can't say that I've ever read a story where multiple sets of Infinity Gems existed.

Well, Hickman's Council of Reeds story line in Fantastic Four had 3 of the Reeds wielding Infinity Gauntlets, but they only worked in their respective dimensions.

See? So you can play multiples (including paying for them), but only one of them actually works

Well, my justification is usually "time travel did it".
What.

Yes balancing is important. Can still have Lobo pick it up and that will work just fine then

What's the Council of Reeds? They're a group of various Reed Richards from other dimensions, introduced in Jonathan Hickman's current run on Fantactic Four. This link explains it way better than I can.

Oh my. So much for Reed Richards Is Useless, huh?

Well, not really. That was kind of the point of the story. "Our" Reed couldn't bring himself to pay the price of basically abandoning his family and friends in order to solve all life's problems. So our Reed is still pretty much useless.