Frankly, MamaTexan's interpretation does seem to be awfully narrow, but to admit much more opens the door to what we have today.
No mere words would prevent what we have today, as the issue is willful illiteracy on the part of several of the Justices.
OK, I can see that. But what it seemed like MamaTexan was saying (please correct me if I'm wrong, MT) is that the clause pertained to actual commerce between the governments of two states, as if those governments themselves were parties to a transaction.
Aside from that, I can definitely respect the argument that the interstate commerce clause was not intended to be a source of federal control of any interstate transactions (governmental or non-governmental), but rather, as you say, a preventive measure against state interference in such transactions. Madison himself made the same argument.
My understanding of the commerce clause is that it was to preclude protective tariffs (or their equivalent) between states. Such could be considered a State transaction.
And there was a federal court system put in place to support that. If two states had a disagreement, they'd resolve in court instead of combat.
But now, the federal courts run around looking for cases. A bird might fly from one state to another so it's "interstate commerce"... indeed :(
That's being mighty generous. Closer to absurd is more like it.