I am at a similar position...
I have been riding a flat bar hybrid for around 12 years - it was a 'put-you-on' that has served me well.
I have an antique 1990s MTB that will have to go to make space, I also have a FS MTB that i havent ridden much but would like to ride more.
Its likely the hybrid will go too, but i'd like to keep it in the short term.
I've arrived at wanting a gravel bike because essentially I don't want a fragile, nervous, long geared road bike.
I've long coveted at
Ribble CGR, but at the moment my head has been turned by the Sonder Camino.
I have limited space for N+ bikes. I want to be able to commute and utility cycle on road as well as be able to ride rougher stuff, things like towpaths, gravel roads, trails etc - rougher stuff that would upset or damage an out and out road bike, while a MTB, even a hardtail doesnt have the legs for me on the road.
It is my ambition to a little more backpacking / cycle touring so i want to be able to fit guards, paniers and carrystuff - if not enter the carrysh1t olympics.
I've been umming and ahhing about a tyres, but have sort of reconciled that i'll probably have a couple of sets of wheels (or if not tyres) to cover all bases. I currently run 700×28C Marathon Greenguards however as they get bigger they get significantly heavier which has given me pause for thought - perhaps ill go tubeless and wont need the extra puncture resistance. The extra volume will be nice :-)
I want Hydraulic brakes, a 2x set up because even now I end up spinning out with 48t -11t. The bike gets used in all weathers and gets hammered. I cant always give it the love it needs so i do end up chewing through cassettes and chains so the less sprockets the cheaper servicing.
All that means I am looking at buying the Camino Frame, bits and bobs and a a Cues Groupset.
The plan going forward is for me to put the plan through the 28day personal cooling off period (to ensure no impulse buys) and then to go and hire one of the CAminos from one of the Alpkit stores to try the size fit / appeal. Its £49 a day an they give you that back if you buy a bike (not sure about a frame).
I guess I already lean more towards the road side than the MTB side, but If you arnt sure perhaps having a bash on a hire bike might be worth it?
This video here made me look more closely at gravel bikes.
View: https://www.youtube.com/watch?v=JL-hYLShoAY
Try before you buy -
https://alpkit.com/pages/sonder-try-before-you-buy