I am a mountain biker and a road rider. Really like the road bikes and have thought about getting a Cyclocross to do the gentle trails offroad. I did at one point convert my old OCR into a more suitable bike for the trails with far stronger wheels and knobbly tyres for the odd offroad link between road routes.
For me that was a disaster. The bike lost the bit of "oomph" that it used to have on the road and on the trails- I lost the control on the rough stuff and comfort was completely lost
Offroad and road are completely different and do require different bikes to get the best out of either. But if you are doing both types of riding- then a cyclocross is a good compromise. But I managed to convert the MTB into a sensible Road going bike by fitting a 1.5 slick and it was still good offroad on dry hardpack with the same tyres and no aggressive riding.
If you are not certain about road riding being your thing- Then try converting the MTB to something that can do Road rides. Could be a cheaper way to find out if you like road riding.
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How long was I in the army? Five foot seven.
Spike Milligan