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

It's funny that the individual selling the innuos zen in the link above is selling the innuos to move to a combo dac/streamer. 

The ONLY reason for the sale is that I am moving to a DAC w/ streaming capabilities and so the Innuos would be redundant.

  He must not have got the separate streamer/DAC memo.

I've always felt a preamp is over kill.  An amp with a volume knob is what I like. Or controlling it from a pc or a source is best.  I feel the more connections with a rca or balance inputs has another transfer signal losing its purity imo.

I agree with your thinking.  I have an  Allnic L-8000 DHT pre it is amazing.  I also have a Lampizator Golden Gate DAC with DHT analog output and volume control.  I stream Qobuz via an Innuos Statement using the InnuOS Sense App.  Its much better than Roon.

Get yourself as good an optical streamer as budget can support from Sonore. Don’t get sucked into the trap of spending more than you need on a quality streamer. Their most expensive option is 5k US. Then get a great DAC like the Mola Mola Tambaqui and of COURSE preamps matter - maybe more than anything else in the chain. I have their Makua preamp and a Cerious Technolgies Lumniscate power cord. Lure Class A Krell power amp. Pure bliss.