This is something we've spent quite a while discussing, and probably will continue to consider. For now, all date range changes occur at the panel/tool level, but I can definitely see why you'd also want it at the project level.
I second Daniel's comments. I really like the analysis workspace functionality but I find it has some usability issues. Comments thus far:
1. The date selection is confusing. How to I select a specific date from the past?
2. Sometimes its a little confusing where to drag columns: Example report:
Today : Hourly : Pages Not Found : Pageviews.
I drag Today, Hourly on the left and Pageviews on the top right. Now to view the pages not found, I must add this dimension to every hour. Once I was able to drag it to some place and it repeted this for each hour, but I can't find it and its not intuitive.
1. For date selection, you aren't limited to just the draggable options. There's also a calendar for choosing a specific date in the past. (I agree with Daniel that the calendar could/should be improved, but it's there!)
2. I see what you mean about this workflow being a little bit . . . off. I think this should be addressed when we add the "table builder" to the tool, which will let you easily arrange and re-arrange dimensions, segments, and metrics before running the query (similar to what is in Ad Hoc Analysis today). But it's a good point; in the current version you need to add things in the right order sometimes.
I can't stress enough that this is beta, and we'll be adding significant new features every couple of months. We'll get these taken care of!