OP, you are nowhere near the limits of your bike's capabilities. Many riders have toured the country on lesser bikes. I have a 1993 Trek 720 set up with a flatbar with a slight sweep and rise and Ergon GP2 bar ends. I've ridden a good number of centuries on it and find it very comfortable. Your cyclocross bike should easily match its performance. If you want a new bike, go for it, but your current bike is no hindrance to doing 100 miles.