Howdy Daniweb,
I've been doing some research and granted, there's some evidence that changing your template design in Wordpress can hurt your SEO, but there's little to no indication that pre-designed / template purchased websites are not optimzed properly, which can hurt your SEO.
Does anyone have any insight to this?

It's down to the skill and knowledge of the Author of the template(s), and of course the SEO writing skill of the content Author.
Your actual content should not be changed by any template, but the Author of the template needs to be aware of the use of specific tags such as h1, h2 etc can impact the way your page is scored, and use/not use them accordingly in the layout framework.
You can probably score a few pages from your website by jamming the URLs into a free online SEO analytic service. Then jam the same pages through using a different theme, and see if there is much variation.
As a main set of rules, you want your page title to match your page h1. There should only be one main heading (h1) on the page (unless it is a blogroll). The subsequent heading tags should have relevant information underneath them; The images should all have alt descriptions; the links should all have titles. All pages/items should have meta description and meta keyword tags.
Any theme should not (but may) adversely affect these main rules.

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