Your 17-55 Canon lens is pure gold and nothing will work better or easier than that on your crop body. If you wanted to add a lens, you could consider the Canon 85mm/1.8 prime, this is a "fast" lens, very quick to focus and very good IQ. If you want a little separation from your "street" subjects and still be inconspicuous, there isn't a better lens than the 85mm on a crop. This option will set you back less than $500.

A different option would be to sell you 18-200 and buy the 70-200/f4 and keep your 17-55. You would have a high IQ, very usable twin lens kit. This would cost you around that $1000 mark.