Does a streamer do anything to the data that Tidal provides?

Let me reassure you. I have a few Chromecast Audio streamers, some using the analogue output from the internal DAC, others using the optical digital output. The digital output uses the mini optical connector into the same little slot as the little analogue output does, in the same way some Apple products do. For a test, see here: http://archimago.blogspot.nl/2016/02/measurements-google-chromecast-audio_27.html
The digital output is a relatively unknown feature. I have heard from several people who, like me, were told in a store that the Chromecast Audio only has an analogue output.
On the software side, I am happy with the TuneIn app. It even has a sleeptimer.

My practical experience:

Depends somewhat on the DAC. I used a Wyred4Sound re-clocker, and it worked really nicely between a Squeezebox and an older DAC.

Since I upgraded the DAC, this no longer matters.

Best,

E

@willemj thanks for the reply.  I'm not sure if the Chromecast Audio is for me as I wish I had the control of the Chromecast Audio using TuneIn and a dedicated ethernet and power plug like the Apple Airport Express.  Does this type of box exist for less than $99?  Maybe I will just get an Apple Airport Express (want one in black).

Not sure what you want with the ethernet and power plug and why. The Chromecast can use an additonal/optional wired connector if your wifi is not strong enough, and it comes with a power plug (in fact the wired connection uses a special net adapter). What it will not do (unlike the Airport Express) is serve as an additional router to beef up your wifi network (you will need something else for that).
One other difference is that the Chromecast only uses your smartphone or tablet to extablish the connection and as a remote. The actual streaming is done directly from your router to the Chromecast. The downside is that if you want to give it a new command that may take a litle while (and not all apps are very good at this), but the advantage is that it does not need your phone/tablet to actually stream, so youir phone's battery is not drained and you may even turn it off.
Finally, the AE is only 16/44 while the CA goes up to 24/96 (if you care about this).

Many thanks for a lot of inspiring responses. I must admit, though, that I still do not understand, how a streamer can enhance the bitstream.
 
If the streamer is a transporter that connects the music sources with the DAC then how can it make the output any better than the input? 

I understand that if the input is provided in higher format than a streamer can manage, then a better streamer can do a better job. But if a cheap streamer can manage the input stream from say Tidal and provide it to the DAC bitperfect, then the job is done - isn't it?