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

I always have spent more my preamps than any other component.    It's the heart of any great system.  Get it wrong and you don't exploit the potential of ANY source component.  

In 2019 I got a Bluesound Vault 2i.    It literally changed my life as it pertains to music.   In 5 years I have discovered  more music than in 50 

For a short period I had the Vault and my DAC connected to the amazing sounding Zesto Leto preamp.   That preamp is world class and sounded fantastic streaming from Qobuz and Tidal

I upgraded to an Aurender N200 to pair with my DAC and feel it was a worth while choice despite it's price tag.  I don't even play CDs anymore .  Maybe a handful every year  

Demo something like a Aurender A200 or better and you will see that streaming can sound pretty good 

First, try Qobuz vs Tidal, if available to you.

To most, Qobuz sounds better than Tidal and way better than Spotify.  I only stream, and would love to make a new system without a preamp.  But, so far, my systems sound better with a quality preamp.

Only a waste if you don’t massively upgrade your streamer and DAC.

I tried DAC direct and it lacked drive and dynamics ,  after owning that Zesto it was clear where all my systems in the past were lacking.   

Installing that elevated my entire system to another level.  Also, it demonstrated how good my Quicksilver monos really were.  

When I connected it to my 300b it really let that amp shine.   A good pre is crucial to good sound.  All sources pass through and it drives your amp.   Most overlooked component in many systems.  

I sold that Zesto to fund a DHT preamp and am using an old Sonic Frontiers preamp.  A temporary major step backwards in sound quality.  Sounds good but no where as good as with a great preamp.

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.