On the other hand, 4% and 6% could just be statistical flukes, *IF* your traffic during that time was low. For those two statistics (pv per visit, time per visit) 4% and 6% are not very big numbers at all.
If you really made an improvement for the end user, you should be seeing 10-20% or more for pv per visit (that's my experience). The bigger the basic traffic numbers, the more you can believe the 4% and 6%. Compare previous 2 week periods to each other - were normal variations from period to period in the range of 5%, or are you now seeing something really different?
If you changed the navigation, the most interesting analysis would probably be comparing the lists of pages viewed to each other. And the bounce rate happening on the changed entry page. Also the time spent on individual pages - (I'm not sure if GA displays this for individual pages though; I don't use GA much).
Calculate the time spent per average page and compare that, too.
What kinds of improvements did you make? Get inside the head of a typical first-time visitor and think about what *should* be different. Were you working toward quicker identification of what to click on? then individual page view viewing time should be shorter. Were you trying to give more direct paths to a typical goal? Then the number of pages per visit should probably be less ... unless your navigation also encouraged them to explore more. Faster loading time? Then time spent per page should be a lot less.
Improved Adsense revenue can be affected by inducing Google to show really relevant ads on your pages, as opposed to semi-relevant ads. People will click on relevant ads more often. You can affect this by adjusting your content's words to tell Google the right things about the content and show better ads. And you'll get better Adsense revenue if people just see more pages that have ads, of course.
Repeat traffic can be affected by lots of things, but finding what they're after is the best way to get visitors to come back next time they want something from your site. Navigation improvements and truly valuable content would be big changes.