My prediction is these devises will start becoming worthwhile when Alexa et al reach actual human intelligence. Voice interfaces does nothing for anyone unless you are handicapped in some way.
I imagine by the time voice assistants reach human intelligence we will be able to ask Alexa to clean the floors and put the food away :)
Hands free multiple kitchen timer and radio/music player has been worth the cost of entry and I find useful on a daily basis.
While I rarely use my Home, Android Auto is incredible. (Although it's still infuriating 5% of the time, it seems to like to make best guesses more than asking for clarification which is super annoying)