If I'm understanding correctly, your two dashboards are in separate workbooks?
You can copy worksheets from one workbook to another (see http://kb.tableausoftware.com/articles/knowledgebase/bookmark-copy-sheet) Unfortunately, this doesn't apply to dashboards.
If you are really ambitious, you could try the following:
1. Copy all the views you need using the above method.
2. Make a backup of the workbook you want to get the second dashboard into.
3. Open both workbooks in a text viewer. Make sure you've saved them as unpackaged workbooks .twb. The .twb files are XML. (Packaged workbook files -- twbx -- are zip files that contain the twb and any data extracts, image files, etc...)
4. Locate the section in XML that contains the dashboard you want. Copy and paste that section into the other file.
It might take a little trial and error and I would definitely recommend having backups. Hope that helps!
I have a question that is very similar to Hunny's, so I thought I might just piggy back off of your explanation to get further clarity on my question. I hope that is okay etiquette.
I am doing a little discovery to see if I can merge multiple existing workbooks into one workbook. It sounds like I could copy the the worksheets from each into one new workbook, but then I would have to re-create the dashboards. There is also a recurring issue with both of your methods in my case in that I will need to refresh the data in my new 'combined' workbook each month - it seems like this may not be possible.