Associate is $80, which is a lot for me to spend if it doesn't work out
Why not experiment with a couple of good free themes first? Just so that you can get comfortable with switching themes before spending any $$.
However, you really do need to upgrade WordPress before you do anything else. Not only is your site currently running a very real risk of being hacked by using an older version of WordPress, but any new theme you try (or buy) may actually be incompatible with your version of WordPress.
How would Associate know which pages and pic to pick up for the home page (the three boxes under the scrolling banner)?
It wouldn't. Any special theme features - like scrolling banners or homepage boxed areas - won't transfer from theme to theme. If the new theme supports similar features, they'll need to be set up again.
And would all my widgets transfer smoothly?
No - widgets have to be set up on a per-theme basis.