I read through this pretty quickly, so this may have already been mentioned.

Cyclocross bikes are more than just modified road bikes. This is one of the articles I read last year when I was thinking of buying a 'cross: The Case for 'Cross. Wikipedia's entry for Cyclo-cross bicycles also gives a great description.

I didn't buy my 'cross bike with the intention to race. Like you, I wanted the fun of mulitple options from one bike and the beauty of a 'cross bike is definitely in the options. Salsa's suggestion of beginning with the frame is a good one. And for a bar, you might consider something I've seen on a lot of messenger bikes lately: an over-sized TT bar. The ends of the bar face forward instead of back and down, so you've got the option of riding on the flats, or stretching forward with a wider arm position than you'd have with a typical TT bar. I'm seriously thinking of trying a pair of these on my bike.