“C) in CA at least, some of these operators are only investing in the toll taking equipment on existing, unimproved road (I-680 from Walnut Creek south is an example)”
The price point for monopoly-controlled roads is much, much, different than for freeways. Once a single, money-making, entity controls the right-of-way, it is obviously MUCH MORE PROFITABLE to simply jack up the tolls, than to add lanes...both accomplish the same - ending traffic jams.
The difference being, of course, that in once case we can seamlessly drive between cities very efficiently (freeways), while in the other case, we become like India and Nigeria, where the uber-wealthy can get around via alternatives, but everyone else wanting to trek between cities feels like the stagecoach guys from 150 years ago.
Raising tolls to reduce traffic congestio is EXACTLY what Houston did. Problem was, there was no other route to take.