I had a 17-85 when I bought a 10-22. The ranges are very different, and consequently the usage. The standard zoom is still a good general purpose lens. You don't have to chuck it when you get an ultrawide, unless you really never use it.
My answer is very simple and so should also be yours and it is "Yes, if I have a need for this shorter zoom." The basis and rational approach to buying should always be buy what one need. So if I have a need for a shorter zoom than my current 18-55, then yes, else I keep my money for other needs. Ya, ya, I know it is easier said than done, however, the fact that you have to ask this question, it is not an impulsive buy. So yes buy it if you need it to cover the wider FOV and/or get closer short.
15-85 is the best choice kind of combination between the two, use for general purposes - landscape, portrait, street life, etc.
If you travel a lot, then buy 10-22. Unless, don't need such ultrawide lens for normal pic lah :bsmilie:
imo, I was once the same as you, thinking that 18mm wasn't enough for the MBS or the scenery shots, but after getting my 10-22, I find that for many things, it became too wide at 10mm and many times for the MBS, my framing was at 15-17mm. If you are going to buy 10-22, I really suggest that you rent it for now and see if you like it or not.
Before 10-22, I was also considering the 15-85 too. But I went with the 10-22, so far no regrets, other than missing some framing at 55-85mm which I crop during PP. That said, I couldn't visualize well enough from a 55mm view to crop the 85mm view.
Both will still be useful depending on what you like to frame into your photo.
This will help to illustrate better at post #8.
I had an opportunity of having 2 cameras, an uwa lens and a kit lens (18-55) when shooting this. 2 photos at 10mm and the other at 18mm. See what you like to shoot and make a decision whether you want to get the 10-22.