I have made many mistake in the past and spent my money foolishly! Go for the best. It does make a big difference. It is better to have one excellent normal zoom lens than to have a bunch of good lenses! You will be so happy and with your style of shooting, a Nikon 24-70 will cover most of your needs. Just borrow one and shoot it against your 50mm 1.8 in differnent environment. I notice that you increase your sharpness to compensate for the poor performance of 18-200. I had to do the same in the past!
You have taken some great pictures! I think that if you try AF-S 2.8 24-70, it will match with your style of shooting! Just borrow it from somone and try it out!