My wife and I really use our camera to take pictures of our young kids in action (not portraits), either outside or inside (often with a 430 EX II and sometimes a sto-fen omni-bounce). We don't do any post-processing, and very little cropping. I'm certainly not one who looks to see who sharp corners are, as i'm mostly concerned with the sharpness of the center. I do use my camera for video though. At the end of the day, I'm probably never going to be a full-frame user, and I probably won't be shooting "in the elements" to where weather-sealing is that important.

All that being said, would a person like me notice a somewhat significant increase in IQ for photos / videos if I went to either:
1)a 70D with 18-135STM
2)a better lense (17-55 f2.8 or 18-85f3.5/5.6) that's still wide enough (the 24-105 f/4.0 probably isn't wide enough with at 24mm).

I'm open to any other ideas <$1,500, but also want to say that I am not one to buy used or refurbished items.

P.S. I also have the nifty-fifty, but rarely use it, as my images with it end up coming out pretty soft (I must have a shaky hand that needs IS) since I never use a tri-pod.

Thanks in advance,
David