Are higher end preamps worth the investment when you are only streaming Tidal & Spotify ?

Qobuz (best) and Tidal can sound as good as CDs, stored files or vinyl given the right system. The sound you get is really dependent on all your components. 
 

Your system is a sum of its parts. I have found that with careful choices topically an optimal system will have all components with roughly similar investments… so streamer = DAC = Preamp = amp.

That said, if I were going to invest more in something it would typically be the preamp. It really is pivotal in setting up the sound. 

With the goal of achieving higher fidelity, would a 10k -12k MSRP preamplifier be overkill when you only stream from Tidal or Spotify?

Yes, the C658 is fine for your current setup. If you want an upgrade measure your room's FR and post it in your profile and we can discuss. Acoustics are #1.

A preamp will bring life to your system.

Don't believe me, ask Paul McGowan.

Bob

Tidal and Qobuz on a great streamer and DAC sound better than most CDs because most CDs are played on a CD player with internal DAC.

Now if you’re doing CD right, with a good CD transport to your same DAC, they are likely hard to tell apart.

Jerry

@puffbojie

NAD C658 DAC Streamer is really a weak link but the DIRAC feature really helps with my room. I might have to get a stand-alone room correction device in order to update the streamer and Dac as the NAD does not allow you to disengage the DAC from what I understand.

I looked for some photos/measurements of your room to see if I could figure out why you needed room equalization, but no photos. I don’t know if I should ask you why you think that you need room equalization, or question myself as to why I think that I don’t need room equalization.