It will probably be cheaper to fix your current bike than to buy a new one. However there is nothing wrong with looking for a new (or used) bike.

I have the 26" LHT and like it. I don't feel fast on mine, but I like the versatility. Smaller wheels are supposedly stronger and quicker to get up to speed in comparison to 700 wheels. But 700 wheels are supposed to roll better and require less effort to maintain speed. But there are so many other factors that come into play that the whole debate takes on different contexts to different people.

My advice is not worry so much about the wheel size but worry more about how the bike feels, how it fits, and what you want out of it. Basically what doesn't your Jamis do for you? You want a faster and smoother ride? You want to carry loads of stuff with you? You want to fit a variety of tires? You want disc brakes for bad weather? etc...