Compromises in a do it all bike?
I'm thinking of what I'll call, for lack of better word, a do it all (or mostly) bike. I need some help understanding what compromises in design or whatever that I'll have to make. The bike would be steel and lugged. I'm in fairly fit shape and an experienced rider (mountain and road) and weigh 155 lbs. I would like a bike that can handle fast road rides, dirt fire road epics, maybe some single track and touring. Admittedly, 99% of the time will probably be the road and dirt riding, but I'd like the ability to mount racks and go on a touring trip. I'm not looking for any kind of suspension. I'll probably enter an occasional cross-race, but I'm mostly just an aggressive weekend warrior.
What are some of the compromises that I'll have to make? For example, since I want to use the bike as a touring bike does this mean that thicker tubes should be used for strength at the expense of weight? My road bike is a custom Serotta and I love the way it fits and handles, but there isn't much clearance for fat tires. I guess I'm just wondering if there's a way to have my cake and eat it too.