Like Hakem, I also work for a company that ranks and reviews cars.
For the most part, the 2008 TrailBlazer is a carryover from 2007 - so you can look at the pros and cons of this year's model to forecast how good of a midsize SUV the 2008 TrailBlazer is going to be.
In general, the 2007 TrailBlazer is criticized for its questionable reliability, poor fuel economy, and dated/low-quality interior. Even so, it's got a decent amount of cargo room for its class - and the SS model's V8 engine performs really well.
What sets the SS apart from the base TrailBlazer is its 6.0-liter V8 engine (borrowed from the Corvette!) and sport-tuned suspension - that, together, contribute to a really thrilling on-road SUV experience. Still, be warned that it is a gas guzzler. In fact, the EPA ranks its city/highway fuel efficiency at 13/17 mpg - and that's just the two-wheel drive!
Still, if you are going to buy a TrailBlazer, your wife's right to choose the SS - because the base model's handling is pretty poor for its class. The SS, however, seems to address whatever handling problems (mainly an unresponsive suspension and imprecise steering) the base has. Keep in mind though - the SS' lower clearance doesn't make it ideal for off-roading… unless, of course, you can afford to be a risk taker.
In regards to its interior cabin - it's a good family car because five adults can fit comfortably and there's a decent amount of cargo room for whatever it is that you're hauling. A lot of reviewers, however, complain that it looks pretty drab - and the quality of its materials are sub-par. Even worse - it doesn't do as well as many of its competitors in government crash tests, although it comes packed with a wide array of safety features.
All in all, I'd say that the TrailBlazer is a pretty mediocre car. While the SS is better than the base - I definitely wouldn't pick it over a Honda Pilot or Toyota Highlander (which cost about the same - but trump it in just about every category imaginable). I suggest you try talking your wife into buying one of these instead.
Hope that helps!