I'll preface this by saying that I haven't test ridden any of the bikes I'm thinking about - it's all been virtual comparisons and brainstorming. Obviously any purchase would require a thorough test ride of many of the bikes I'm thinking about and the appropriate geometry comparison for any special order bike.

Although I won't be buying for several months and maybe up to a year, I've already begun the research and would like to elicit a few opinions.
Currently, I have an XL 2006 Specialized Sirrus as my primary bike and sole commuter. My wife has a 2005 Trek 7300 in a 20" frame that I can ride comfortably, but I would only use a temporary back-up. I've got the Sirrus outfitted with rack, fenders, panniers, lights - the standard commuter package. I currently run 25 mm armadillo tires and have not had a problem, but if I get a second bike for the below listed reasons, I'd consider running a little wider tire as this bike will pretty much be completely dedicated to commuting. I commute 3-5 days per week and do 1-2 fitness based rides per week on top of that (usually 15-25 miles) right now.

Anyway, I'm looking for a second bike primarily for afternoon training rides with a couple of cyclist friends of mine (both are cat 3 racers) and longer weekend rides. I'm not looking to race anytime, but would consider doing event rides or centuries in the future. I live in the greater Houston Bay Area and it's extremely flat with just a few offroad options in the area, therefore the vast majority of my training will be on the roads, which are ok. There is still a lot of road debris, potholes and rough stretches on the roads around here though.

My initial thoughts were to buy a racing bike such as the Specialized Roubaix, Jamis Quest or Trek Pilot. Something designed with comfort and speed in mind. While this makes a lot of sense for keeping up with my cyclist friends, works fine for training rides on the weekend and would likely be fine for a century, it leaves me with the least versatility in my second bike.

So, I considered a touring bike such as the Trek 520, Surly LHT, Bruce Gordon BLT. These bikes could convert into my commuter at some point, would allow me to do some touring at some point (this is at least 10 years away - I've got a 2 year old and another due in a week or two), and would work well for event rides or centuries and would even allow for some rougher riding conditions compared to the racing bikes. But the reality is that I won't be doing any touring for a long time and already have a solid commuter that I really like, so this seems like not the best fit. Still, it's worth considering.

Finally, comes the cyclocross bikes such as the Surly Cross-Check, Jamis Nova, Kona Jake the Snake, Trek XO-1. I really like the idea that this bike could be used a commuter some time down the road, could be used off-road (I'd like to do some off-road riding, but this would only be for a fun change of pace and is not a priority) and overall would still be fairly speedy on the road although the gearing isn't optimal for pure road cycling.

Honestly, I don't know which way to lean and I luckily have all the time in the world to decide, because I don't have the cash right now - I will in the future. I'm looking primarily in the $1000-$1500 land and would like to at least have 105 components. Given a very convincing story I'd consider going up to $2000, but I'd prefer to use those extra hundreds for appropriate accessories.