You need a bike in order to ride, so yes, the right bike is the one you will ride (or perhaps for many people, the one you would ride the most, since many would ride SOME on a bike that isn't quite right, just not as much).

You don't need a computer to ride, though, and most will ride whether or not they have a computer (if they have the right bike). So a computer is better than no computer if it makes you ride more. If it doesn't make you ride more, then it is all gravy, whatever makes you happiest.

I generally don't ride with a computer, but in my dream world where I get some luxuries, other than speed and distance, the two things I would like to know most are heart rate and the grade of the road, and heart rate would be number one. I can easily live without a computer, so long as I don't get my heart rate so high that I die, and so far, I've only had a few instances where I stopped out of caution because I sensed I'd let my heart rate get too high -- it would be a nice luxury to avoid those times.