Yeah I think the dust I'm seeing is tiny. Sucks that insignificant dust results in no sale or reduced value. This is about the only thing I don't like about this lens. It's by far my most useful lens. I thought of selling it and replacing it with a 24-105L just for the weathersealing. Still debating with myself what upgrade path to choose. Should I just sell it and get the 24-70 II? Is that where I'm gonna end up anyway?
Take your time cleaning it, and you'll get a good result if the dust is between the 1st two groups. I only bothered cleaning those two surfaces while the lens was disassembled. I'd pop in the front element w/o putting the screws back in and zoom/focus the lens to move the elements around. Then recheck to see any dust is visible. I cleaned the front surface of the front element after it was screwed in. All lenses can get dust in them, but I find that having a filter on the 17-55 all the time helps a lot because the front decorative ring that covers the front screws is not airtight.
And yes, you will eventually end up with the 24-70 II. The question is when.