CF does plently of things wrong, but the trash cans don't affect the park experience in the same way that factors like high food prices do, because they don't make the guest feel unsatisfied and ripped off. As for a park's apperance, the trash cans do virtually nothing the atmosphere, at least from my point of view. I certainly never noticed the large amount of trash cans when I went to Cedar Point as part of the GP, and I don't really notice them now as an enthusiast. I do however notice things like litter on the ground and other cleanliness issues. The trash cans (as do the sweeps) generally do their job well and keep pathes clean.
I think it's things like the immense amount concrete that stand out more. That's somthing I've always noticed at CF parks, and a lack of trees is very detremental to a park's atmosphere. I'm certainly a bit worried about the addition of Shoot the Rapids at CP, because they tore down a lot of trees in what is pretty much the only significant forested area on the penninsula. Besides the concerete, the lack of theming, worn buildings and faded paint also are signifcant eyesores which I find eye-catching.
It's the same way with the ads on coasters at SF. Execpt on the prehaps the most popular rides, which usually draw from visual factors to implore a bigger "experience" than sencondary attractions, they do nothing to take away from the apperance they are far less noticible, espically since there are already ads practicly everywhere else in the park.