It looks like the Restful Legs stuff is homeopathic. May be worth trying, but if it doesn't work I would also look at the possibility of a deficiencies in magnesium or iron. Have these been tested? Many people, including one I live with, have found restless leg problems eliminated with magnesium supplementation. It is a common deficiency.
Personally I would be VERY hesitant about attributing pain to "growing pains." We heard this explanation with our son but when his metabolic problems were treated this totally went away suggesting that "growing pains" was a garbage explanation that was getting in the way of treating what was really going on. I would not see muscular pain as separate from hypotonia, but instead a flag that he may have some underlying problem that requires treatment - not just masking with an antidepressant.
As far as waking you in the night, I see that as a huge problem. Your sleep is important too. He's old enough that he should have tools to handle it if he is having problems in the night without having to disrupt your sleep as well. I would focus on helping develop some routines during the day to handle these times. It may help him to get up and walk or to use a heating pad. During the day he may practice deep breathing or relaxation exercises. Rehearsing ahead of time makes it so the body is more able to access these techniques when they are needed.
If you and your son have not already done so you may both benefit from reading more about insomnia and sleep disorders. Pretty much everything written about sleep problems emphasizes the importance of consistent routines. Sleeping in to try to make up lost sleep doesn't work and will make the problem worse the next night. This is a very academic book but your son is bright and this may be helpful to him.
http://www.amazon.com/Promise-Sleep-Medicine-Connection-Happiness/dp/0440509017/ref=pd_bxgy_b_img_c
