Personally i would say "sod it, get a road bike".
an MTB is extra work. some say you have to go further on a road bike to get the same workout from an MTB but
THAT IS THE WHOLE POINT. You just don't get anywhere on an MTB and you see the same boring roads over and over again. on a road bike you and your mrs will be able to go for more miles in half the time, see more and enjoy it more.
i had an mtb for ages and only ever used to do about an hour on it. after my work moved me 17 miles away i decided to get a road bike and commute, and i LOVED the difference in the speed and ease of riding on the road. it was the start of my "cycling career" as i now know it and now i will happily go for a 30 - 50 mile ride at the weekend depending on how much free time i have, and have even done a couple of london to paris rides. i can't believe i wasted my money on mountain bikes. eventually that road bike gave up the ghost and i bought a better one, but that bike will always have a special place in my heart
in fact, the frame is still in my loft, haven't got the heart to throw it out.
So buy a road bike and see the world. it doesn't have to be an expensive one.