Currently I connect my iPhone to a Marantz CD player via its USB input. It's connected, via coax, to the DAC in my amp. I can listen to the popular streaming services like Spotify, Pandora, Sirius, Amazon, and Apple. What would be the benefit of paying $500-$1500 for a dedicated streamer other than the convenience of not using a chord?
The short answer to the title thread is Yes...a dedicated streamer is a convenience. Many of the modern AVRs have Pandora, Spotify, etc that you mentioned built in.
It largely depends on what you're streaming, do you have a library?
For me...I have a decent size itunes library...(mostly mp3 files)...I have playlists that I playback on the whole house system. I also have a growing SACD/collection and still occassionally will buy CDs.
Storage...I think I will be signing on for the Qobuz hifi subscription to expand on what I have, but personal library storage on the streamer is important to me.
Playback capability...the world of multi-ch hi res is understated, but imo is just as "next level" for studio recordings as Atmos is for the movie track. If your streamer can't process DSD, 24/192 and other hi res formats, I think as a serious music lover you are leaving the opportunity to explore on the table.