I agree with your first point.
But Sam will only play 2 matches in Fed Cup, the players from other 3 matches will much rather prefer playing at home than in another country in an environment which will definitely support their opponent.
At this point in time you are probably right because its unlikely that we're going to have a big main draw presence there outside of Sam.
Where Jarka's ranking is at the moment, and unless she goes on a tear somewhere, Id expect she'd see Fed Cup as priority than battling the clay quallie rounds. Rodionova the same, if she gets picked. Both seem to have a strong committment to representing their new country.
I think Casey last year played those articifical grass Japanese tournies in preparation for the French, either way, has never prepared that well for the clay anyway.
I think Liv was playing the two clay 25k's in Australia last year.
Barty has to manage her limited schedule and would be happy to get the competitive play than having to train somewhere overseas.
Always been a gripe of mine that the girls don't play enough clay tournies and stick too closely to hardcourts when they can, so I expect they won't be fussed to be in Australia at this time.