From my point of view and learning I think I will only get to the point you want to get to from a year or so of using photoshop. I know what the renders and stuff do, know about a few techniques but the rest I get from tutorials and they either stuff up or don't. I can't always remember what I did in a tute so I wing it most of the time.
I found some tutorials don't use the shortcut keys like ctl B for colour balance and only one tute I have come across even uses colour balance, the rest use hue/saturation to colour the image.
My shortcut keys won't even work now for some reason unknown to me.
Inspiration is something I lack for example last night. I tried like 4 times to do a sig with the theme of 'summer' and still couldn't come up with anything.
The brushes I don't really use and prob have only once cos I suck at it and I kinda want to impress hobo so gotta stick to abstract
lol he doesn't like pics in sigs either so I try keep that to a minimum.