Cache dashboard results to improve performance when switching tab?

My first area I would want to focus on is how to improve the loading performance of the slower CVs,  What things are slowing them down? Things like too many rows/columns and member formulas that are dynamically calculated can adversely affect reporting performance, the latter being significant in it's effect on query performance.  15 seconds to load a CV seems excessive.

yep, sounds pretty typical.  And probably a good reason for all.
I'd be looking to pre-calc those variances into stat accts.  Usually no need to calc them every time the CV loads.  It might be surprising how much that helps.

I agree with you, it would be nice to cache parts of the dashboard so every click isn't a full round trip reload to the server

It takes a little more effort to set up, but have you considered radio buttons?  They should improve your overall performance.  Also, they don't continually revert back to the first tab when you refresh.

I'd say there are two main approaches:

1. As RobbSalzmann said, one can turn those dynamic calcs into stored formulas. You add a little more work to your calculations/consolidations, but you gain in reporting speed. This can be game-changing on some views.
2. You could export those views to reports, then display them as embedded files in the dashboard. No calculation, only visualization. If they don't need to actually interact with the numbers, this is a simple option.
3. Another, somewhat more convoluted but potentially less invasive approach, is to pump those calculated numbers into another database, and then report from there. At the end of the day, a CV is just a table... To export it you can use FdxExecuteCubeView or custom SQL, triggered by some automated job; and then you can retrieve it with regular adapters and stuff it into a BiViewer or Pivot Grid. The advantage of FdxECV is that maintenance of the layout logic remains in the CV itself.

They are both legitimate approaches, each with pros and cons. What to choose will depend on specific considerations for each Cube View.

So radio buttons should only refresh the page you're on...whereas tabs try to refresh everything.  This is where I think it could provide some time savings for you.  

When you set up the component, you define the buttons options with a param.  Typically I'd just use a param type = delimited list.  The param can be hardcoded with the various options, or can contain variables if you want the list to be dynamic based on other selections.