Your cruiser is plenty well built for the trails here. Other than the few extreme trails (carnage, independence, billings/ bangs canyon) you'll be fine.
One thing to note though, I moved here from Louisiana in 2007 and had my rig set up for boulder fields, hill climbs, and mud pits.... Around here there is almost always an off camber spot on every trail. Had to change some things on my rig to lower it and get some balance going to keep it shiny side up. The formula for colorado is as little lift as possible with cutting to fit tires, lots of skid plating, and more down travel than up travel. Also, some mud terrain tires do ok in the ice and snow, but for the most part, more aggressive All terrains seem the work better. We just don't have any mud. The coopers, BFG's, and lately Goodyear duratracs are king. I had some Remington mud brutes when I got here, and had to get rig of them immediately because they wouldn't hold the traction in snow and ice at all.
FJ40's aren't exactly known for low center of gravity stability, so you might consider a wider track, or smaller tires. Suspension flex isn't all it's cracked up to be, so don't get caught up in that, though it sure can help with stability going through the washouts and rock cracks. Some people don't realize how remote things are in colorado and that cell phones rarely ever work, so focus on reliability
