Unique Contextual Content

[poke1]

Let's say you have a page on your website which displays the current discounts available for iPhones. The page is a list of deals with buttons to reveal a promo code.

Would adding contextual content to these pages improve rankings?

If the main keywords are already on the page, such as "Save 20% on iPhone 5 with this great iPhone coupon code" where iPhone coupon code is the target keyword. Does it still make sense to put 500+ words of contextual content on that page, even when the content isn't really something the viewer cares about?

I've noticed websites doing this, and ranking well. I wanted to know if this is a significant ranking factor or just a coincidence.

[HiveDigitalInc]

Topical relevance (LDA) has been positively correlated as one of the strongest onsite rankings factors (https://moz.com/search-ranking-factors/correlations)  and as a result has been a driving factor behind sites adding additional contextual content.   In my experience, a well ranking site likely has a higher contextual relevance because it has comprehensive content on the topic demonstrating subject matter expertise...

As SEOs, we typically mimic those strategies that we know high-ranking sites have implemented in an effort to gain higher rankings ourselves.  For business that aren't subject matter experts, and simply add contextually relevant content, the result isn't often improved rankings for the target keyword (e.g.  iphone 5 coupons), but instead is an increase in the overall traffic to the site as a result of a broader set of long-tail keywords with rankings (get discounted iphone 5, best deal on iphone 5, etc.)