Interesting commentary. I have definitely used clonidine for ADHD and definitely seen it be beneficial. I particularly use it in kids who have had in utero substance exposure to alcohol or methamphetamine who simply haven't tolerated stimulants at even micro-dosages because they send them into aggressive rages or make them irritable and intolerable. I have several handfuls of kids who have done quite well on clonidine as monotherapy for ADHD (e.g., young children, children with in utero substance exposure), but I tend to use it adjunctively. That said, I typically use Tenex over clonidine because it is less sedating, but in a kid with insomnia who hasn't benefitted from melatonin, I might go with clonidine first.
I also tend to use alpha agonists in very young children with ADHD when they're not going to tolerate a stimulant--say 3 and 4-year olds who are so hyperactive that they are exhibiting language delay and can't work with a speech therapist because they're bouncing off the walls like a ping pong ball. 0.25mg of Tenex can be your friend, and it can be quite effective. Give them even a milligram of methylphenidate, and you run the risk of seeing dilated pupils, hyperactivity and aggression. Clonidine and Tenex are also helpful for tics, whereas stimulants can be the exact opposite.
If you look at meta-analyses, clonidine actually has a decent effect size of 0.58 in the treatment of ADHD.
http://www.ncbi.nlm.nih.gov/pubmed/10596256
Prazosin is extremely effective for nightmares, and I found that working in a trauma-focused residential treatment center that I rarely came across an adolescent where I couldn't get them sleeping and get rid of their nightmares with it in short-order. I have seen Tenex and clonidine both be effective for hyperarrousal during the day for adolescents with PTSD, but I don't tend to use prazosin for this given its limited half-life.
Just one man's experience as a child psych. I like the alpha agonists and use them regularly.