I recently had the same dilemma of wanting a different feel for my hybrid/comfort bike. I found out, unfortunately, that you cannot substitute a road handlebar in place of a mountainbike style handlebar without replacing some or all of the related components. It sounds like your current bike has served you well and perhaps upgrading the parts that are failing you could help. But I wouldn't goof with the handlebars unless you're willing to drop a bunch of money into it; best thing to do in that case is get another bike altogether.

However, 45 minutes isn't enough to justify a new bike, unless the new bike gives you the motivation to step up your workouts to a longer time or more effort.