It's strange how different sports have different fan support at different levels. I'm looking at this purely in the context of Australian sport, by the way...
In cricket, it is virtually all focused at the international level, with very little interest in domestic or club level games.
In rugby union, international games are the pinnacle, with healthy levels of interest for the super 15s and club games ignored by the vast majority.
In rugby league, interest is predominantly at the club level, with state of origin being more popular than international games.
In AFL, there is nothing beyond the club level, unless you count playing a few games against Ireland with totally different rules.
And with soccer, people are mostly interested in internationals and European club games rather than the A-league.
I guess it comes down to two things. People want to see the best players, and they want to see a fairly even contest.
In rugby league, Australia dominates pretty much everything, so most fans don't take it too seriously. If England or NZ were to improve so they could match it with Australia on a regular basis, interest at the international level would probably rise. State of Origin gives the even contest (ignoring the fact QLD have won the last 6 series). Club level is still decent quality and the structure keeps most teams on a level basis.
It is a far more extreme case for the AFL. Australia doesn't have any competition at all on the international level, so they have to make something up with Ireland.
In rugby union, club games aren't of high enough quality (or is it just that they don't have the right marketing?). Super 15 gives good quality and a decent contest. Internationals are the best quality and give a similar contest to Super 15.
And in soccer, most don't care about the A-league because the quality of the players is nothing compared to the European games.
....
So after all that waffling about other sports, what is the implication for cricket???
I guess if you wanted to improve the interest in state level cricket, one day or four day contests, you need to market it right. If the BBL expanded to 16 teams, you could say that the state teams would have better quality players. Treat it like State of Origin - state against state, mate against mate...
But I don't see no crowds at Sheffield Shield games being a problem. If it makes a loss, so be it. It is an expense necessary to have a decent test team.
And if the BBL gets the kids interested in cricket, and they start playing, what are they playing? Cricket! It doesn't matter the format. It's not like you need to 12 year old kids playing 5 day games for them to develop a love of test cricket. Just get them liking cricket first, and as they mature, enough of them will also develop the taste for test matches...