@a0128958, which Irritrol model were you using previously? I'd be interested to know the results after a month of two of use. Perhaps you could give us an update?
Just curious, when is this tour? If the tour has a website, I'd love to learn more about it.
Who is your water district/utility? We can check into rebate requirements in your area.
Good question. As @franz mentioned, cost is a major hurdle for most sensors, especially if needed for every zone. Most SMS controllers, use one sensor for the entire system. Please see this link for more information on the difference between ET and SMS controllers.
Per the 6 reasons you outlined, #1, 2, & 4 would be the top 3 reasons I think wired moisture/soil sensors are difficult to use. The Iro does integrate with the Toro Soil Sensor, which operates like a rain sensor (wiring installation with the Iro found here). I don't believe this is what you're looking for however, as it doesn't report back any data -- only interrupts the common wire.
@msdowdie, did you mean to say ...having to wire them into an existing system...?
Just curious, how much would you be willing to spend on moisture sensors for your lawn?