This is what works for me. After I installed the new iWork updates I created a folder on an external drive & named it "other applications." I then moved the new iWork apps to this folder & renamed the applications Keynote 6, Pages 5 & Numbers 3. I have icons for two versions of Pages & Numbers (I rarely use Keynote) in my Dock. Even with two versions of Pages & Numbers running, double-clicking an existing file opens in Pages 4.3 or Numbers 2.3. This should also keep the Mac App Store from nagging you to update.
Not sure whether Apple fixed something or I did. But here's the story.
I upgraded to Numbers 3 as part of the migration to Mavericks.
I found that Numbers 09 was still installed and it worked fine.
I renamed Numbers 09 to "Numbers 09" and renames Numbers v3 to "Numbers v3"
That caused no issue by itself.
However, I could not change the default for opening .numbers to Numbers 09. It always went back to Numbers v3.
I uninstalled Numbers v3 by dragging the app to the trash and emptying trash.
Then I got bugged to reinstall Numbers, which I ignored.
After a couple of days I was greeting with the notice that a new version of Numbers is installed.
However, the .numbers files are opening with Numbers 09.
I'm afraid to run Numbers v3 for fear it will reset the default program, but at least I can ignore it for a while.
Thanks to all!