those are all great questions.
just know I've watched the 'voluntary' part of this in play in Kansas..and frankly don't know if it's even slowed the advance of these things down.
now, are they undesirable invasives? oh heck yes... on the other hand... are they the 'thermonuclear problem' our govt puts them at? that is an amazing political football in and of itself.
there's a great paper I read (from a researcher in Ohio) that looked at the costs of cleaning these things off intake surfaces...and the numbers get pretty big pretty fast. What is hard to get out of these papers, however, is not the TOTAL cost of the efforts...but how much MORE on top of what is already done as routine maintenance is needed. The numbers, in that case, are a heck of a lot less.
but that's the way these 'accounting games' are played.
why can't we have calm, common sense conversations and workable, practical solutions any more?
In my area I can be ticketed for transporting a livewell full of water. I think in MN you can be ticketed for transporting (failing to clean off) vegetation before leaving the body of water..the solution is simple....clean, drain and dry in the parking lot.
One area that is flat over-looked by everyone: carpeted bunk boards. if I wanted to design a better environment to transport veligers...not sure I could do so...but no one looks at it...we all turn a blind eye... just saying, if we were really intending to be serious...even in a wash down station, you can't get to the interface of the bunkboards and the hull.
it's an interesting new world.
and yes, I bet you are correct that at some point, it becomes an 'income stream' for another govt entity. From which they can hire more folks to prosecute/ticket...and grow it. Just like most govt programs.