I don't know about grapes, but as a non-irrigating grain farmer, I could see attaching something like this to a few plants to keep records on general plant heal

I don't know about grapes, but as a non-irrigating grain farmer, I could see attaching something like this to a few plants to keep records on general plant health in a given field. While there is little I can do if the plant is under stress, I expect the data can be correlated to final yields, which has the potential to improve my marketing abilities. But as you point out, it comes down to dollars and cents.