I currently own a flat bar, hardtail 29er MTB. I can pretty much ride it anywhere. The thing is I usually ride on tarmac anyway with some gravel segments if I take a shortcut through the woods. Where I live is very flat, not many hills etc. Most of routes are paved, there's some gravel/dirt roads. I quite like riding off road as there's no car traffic, but a lot of my riding is b roads with asphalt anyway. As a result I'd tried a proper road bike and I'm pretty convinced that I want to ride something with drop bars. Eventually I want to ride 100+ kms on weekend days - I've actually done it already and it wasn't too strenuous.
My dilemma is whether I should get a proper tarmac race machine with aero features, tubeless clinchers, aero spokes etc and keep my MTB for everyday rides or should I replace my MTB with one size fits all gravel or CX bike (I might get two sets of wheels perhaps).
If I replace my MTB, I have a higher budget, the bike is more versatile, gravel bikes have hooks for bikepacking and wider tyres, it also probably means I have budget for disc brakes. The only reason I don't want to go that route is that gravel bikes are rapidly evolving - for example 2019 Trek bikes have a form of rear 'suspension' (ISOSpeed?) but no such feature on the front, so lots of current gravel bikes feel like a work a in progress and next years models are bound to be better. On the other hand endurance type road bikes are pretty mature and IMO you get better components in a given price range. My typical routine is 2-4 hours riding on weekdays with occasional all day riding on weekends. At the moment I am pretty serious about my cycling hoppy and want to reward myself with nice hardware.