Why Purchase A CD Player or Transport ?

Are there a substantial number of well recorded performances recorded on CD which can’t be found via streaming services, or where the streaming version is sonically inferior to the CD?

No, but the ones that I have — probably around 20 CDs or so — are quite special and I need to have a way to play them. 

I'd never go back to cd's, and I have well over 2.5K of them. I've found streaming superior to cd's, and this in earlier days of streaming to which I've since made further upgrades. Last two transports I used were Mark Levinson #37 and modded PS Audio Perfectwave memory. Add the nearly limitless availability of music via streaming, slam dunk for streaming IMO. With $4k you're well on your way to very nice streaming setup.

I'm already setup for vinyl and streaming..but I might move to the AirLens from the iFi Zen Stream when out and Esoteric E-02 Balanced phono preamplifier from the Sutherland 20/20 LPS once available later in the year.  No real obstacles to building either formats, except the financial hurdle.

All the time doing research and trying different devices is extremely interesting to me, complexity is fun, I understand this may not be for everyone. And as Cleeds mentioned it doesn't have to be difficult, very nice setup can be assembled via tried and trued methods involving minimal complexity.

I'm a huge advocate for streaming, can't put into words how much my listening experience has improved since streaming. Not just sound quality, but also the ability to choose with just a few presses of buttons music to fit your particular mood at that particular moment! My listening session ebb and flow, stream of consciousness takes over.