I have iWork '08 and Pages '08 version 3.0.3. Do I need to buy Pages '09 to work in iCloud?

I'm pretty sure you do. Try this test first: Open the Pages app you have. Click on Help in the menu bar and enter iCloud. See if you get any reasonable help about using iCloud with Pages '08. I suspect you will not.

Purchase Pages '09 through the app store.

I am also considering whether to buy iWork '09 or not. But as it is almost 2013, I wonder if a new version of iWork will be released pretty soon... So I would rather wait...

Note that the product is iWork '09 but the current date is '12. This strongly suggests that iWork '13 is as likely to be released as iWork '10, iWork '11 and iWork '12 was. As we say in my stomping grounds, "Don't hold your breath."

We are not allowed to speculate in this forum about things Apple might or might not do in the future.

But if you look at the history of Pages, Numbers, and Keynote, you will see that recently all three went through fairly major upgrades to add new features (such as revision tracking), and to stay in sync with iOS releases and iCloud. So Apple has been maintaining and updating these products.

Draw your own conclusion about what you're losing by not jumping in.

Finally, I purchased and downloaded Pages and Numbers. I went to a Numbers workshop at my local Apple Store and found out that Numbers is a lot more fun and easier to use than Excel. I love Numbers! 😀