Yes, economically, at the moment, it's hard to justify. But some solar system inverters support wind inputs, which means the "overhead" costs (inverter, battery, etc) drop away.
Yes, in terms of kw/$ adding more solar makes more sense. Except that solar is obviously dependent on sun. Mixing inputs means more "spread" in generation. (Obviously night time, rainy days, and so on.)
So its not just about kw/$ but also smoothing generation to reduce overall storage (which is -very- expensive.)
They do need more maintainence. And they contain more kinetic energy, so failure could be more serious.
These are all excellent, well accepted, points. And just when things are absolutly-positivly a bad idea... well, that's why it's ripe for disruption.
Unfortunately, all the interesting details are pending testing which they've partnered with universities for, but I'm not sure how far along they are.
Its unfortunately very hard to yell whether it's actually interesting or just appears to be so because key details aren't known, but hopefully we'll know one way or another within a year or two.
The other energy source that's drawn my interest recently is microhydro solutions, but that necessarily requires specific geographic features (a water source and elevation).