I haven't had any real problems with MG soil. My plants are pretty big, they could be a lot better if I didn't have them in pots though. Next summer I'll just take a whole bag of miracle grow, and dump it into a hole in the ground and let my plant grow out of that. MWhahahaa. Although my plant's aren't perfect they have a few yellow leaves once they get big, just like last summer grow a few yellow leaves on that plant, but they did produce a decent amount of bud. I don't see anything wrong with it especially if this is your first grow, or you're just regular weed.
I guess it comes down to how much you want to spend. Don't mess with miracle grow fertilizer though you can find lots better fertilizer for around the same price. Like fish emulsion.