Someone pays for the vast grid infrastructure. Right now, it's part of the utilities' capital investment, along with the power plants, and they pay for it out of what they charge for their services.

Should solar panel users expect to not only use this infrastructure for free, but get paid as well for the power they produce in excess of their own needs?

A good solution might be a "maintenance fee," which would be a small percentage of the money paid to solar panel owners for excess power as their contribution to the maintenance of the infrastructure. Arriving at the amount would be complicated, and probably be factored on the depreciated value of the infrastructure, not what it cost in the first place. It would also have to reflect the actual percentage of infrastructure devoted to purchased solar power, which even now, would not be much compared to what the utilities pump into it.

Somebody has to pay for the wires, and it should be the ones using the wires to make money. Up until now, it's been the utilities. Now, it may have to be a mixture of utilities and private generators.