Some notes from 2009:
The Trails Illustrated map shows (correctly) the trail going up climber's right of the creek. But the trail goes all the way to Meeker Ridge.
In other words, if you stay on the trail you'll go straight to the saddle northwest of Lookout, not the Lookout-Horsetooth saddle northeast of Lookout.
This is a pretty dense forest by RMNP standards (reminded me of the PNW) and we didn't see the trail to the Horsetooth saddle when we climbed Lookout. It's likely to be a good bushwhack. From the Meeker-Lookout saddle, though, it looked like it would be an easy traverse over to the Lookout-Horsetooth saddle. (But we didn't do that, and can't say for sure.)