The thing about an IC in Romania is that you will use it for the first few German turns only. Yes it will help you somewhat to set up your Barbarossa, (or you could do some Caspian sea thing), but you can get similar results by just building units in Germany w/o spending the IPCs on an IC (spending more on units). Once you push into Russian territory you will use the Russian ICs, basically rendering an IC in Romania obsolete by the 4th-5th turn. Plus an IC built in Romania G1 (especially a major) is like the Brits breaking an intelligence code and they know exactly what you are doing (good bye Italian navy, and hello Egyptian IC).
If I’m going to spend IPCs on an IC I would wait until I have Western Ukraine (it should fall quickly), that way any units I build in W Ukraine and Ukraine could be with-in striking distance of Moscow. You don’t need more units to push into Russia, but you need more units to finish them off. That way if the allies fly a bunch of ftrs into Moscow you can build more units at the front, Romania isn’t going to help you in the later stages of your Moscow campaign. The only possible help a Romanian IC will give you later is if the allies try to come up though the Balkans mid game.