Welcome to SolidWorks forums Kent.
Not sure if this would be a right place to say anything since we're still under NDA for SW2013. SolidWorks new release is generally around the end of August or early September. It would be hard to comment anything on the compatibility though.
You might also find this post helpful for your future reference
Sign up for Beta, download SW2013 and test it out for yourself.
We are all under NDA and can't comment in the public forum.
Take your question over to the Beta forum and ask it there.
Unless Inventor 2013 is already out, it seems like you would have to enlist in both Beta programs to get the answer.
Suppose I buy SolidWorks (including Simulation) 2012 now, and 2013 is released a couple of months later, will I have to again pay any extra amount to upgrade? Or should I wait for SW 2013 to be released?
If you purchased a licence of SW with subscription support, you will be eligible for whatever versions & SPs become available within one year of the purchase date.