One point that may be worth mentioning concerns the prominent headwall part way up Horse Creek Canyon (a fairly short way after the maintained trail ends at the wilderness boundary, if I recall correctly). The main use trail forks left (east) here, switchbacking up a talus slope; some large ducks lead one to believe this is the most commonly travelled route. The trail here continues to wind its way up above the creek, taking one needlessly high; I gave up on this after 10-15 mins, and made my way back down to the creek, meeting up again with another use trail.
A much quicker route forks right from this mini junction before the headwall, crossing to the other side of the creek. This is the route you'll probably take naturally when descending the canyon, but is easily missed during your first time heading up the canyon; trip reports and my observations of hikers here (including myself) suggest that almost everyone contributes to the misleading trail to the left.
Yes, I went the wrong way up as you described, and found the correct trail when coming down. The headwall is before you reach the third meadow. The correct way is to the right of the small buttress (in front of the peak in the center) in your picture.
agreed. see the commentary on my website on this very point. (fifth photo down the page)