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

Why not consult with Dan Wright? He can send you one of his preamp or the newest Analog Bridge to try it out. Whatever he suggests, it will be a great match for your KWA-150. 

I agree with others, a high quality preamp is indispensable. 

A preamp is little more than switch with additional tonal insertions. Assuming that the highest 'fidelity" is "straight wire with gain" why add an unneeded switch?  It might sound "better" but cannot possibly be more "fidelitous."

I've had Tidal and Spotify. Dropped them for Qobuz. It DOES sound better to me.

 

@lalitk yep, Dan’s equipment is awesome and a great value but am in the used market unfortunately. I am keeping an eye out for his stuff. @ vonhelmholtz yeah that 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.

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.