You can't figure out what each niche ad is paying (unless maybe you use some expensive ad tracking script which I've never tried). Here's what you do with your AdSense channels (one for each page):
As often as you're willing, create a spreadsheet listing how much traffic you got, how much you paid for it, how many ad clicks you got, and how much you earned. Do one row for every niche page. Add a column to calculate how much each visitor is worth to you (earnings divided by number of visitors). There are lots of other handy things to calculate but that's the most important number.
If you're getting a great ROI for a niche (each visitor is worth 3-10 times more than you're paying) you can look at bumping up your bids. But don't just do it senselessly. If you're already in spot #1, moving up your bids is a waste of money. It's also a waste if you're in spot #10 and you have to pay an extra fifteen cents just to hit spot #9. Do it when you think it will bump you far enough that the increased traffic will more than compensate for your slightly lower ROI and increase your profit.
By the way, I do all this with a spreadsheet instead of looking at the AdSense (or in my case YPN) stats because that way I don't have my own pageviews or search engine spiders or anything messing up my stats. So for counting my visitors I don't look at my YPN impressions count, I look at my 7Search stats.