tlw is correct. V9 and V10 (along with older versions if you still have them and not upgraded) will exist on the same machine.
Marled is also correct in that there was some serious issues with V9 and V10 being on the same machine when V10 first came out. It did cause a lot of people here grief. But Waves support worked it out and as far as I know, no one had to pay to get the fix.
Kman88 no the plugin will work as long as you want them to. You won't ever have to pay to upgrade them so they will work. What you pay for is a newer version of the same plugin. And the ability to sell/transfer the plugin if you choose.
Also Kman88, there is not a dud plugin in the Gold bundle. They are all great plugins. I have lots of Waves plugin and don't regret the purchases. Most were made after the prices started going way down. I don't think I paid full price for one single Waves plugin. Money was well spent. Excellent plugins.
A little advise Kman88, get the Gold first for $99. That's a no-brainer price. See if you like them and the install/licenses process. Then if you find you want the SSL collection, wait for a sale. It will happen, just give it time and wait for the time to pounce!! That SSL collection is really good. You will hear a difference.
And like Mark says in post #8, the CA-2A is just as good as the rest of the emulations anyone has. So if ya got it, stick with it.