We had the same issue! There was a lot of desire to optimize everything, which, of course, is nearly impossible for that many pages and content that can be so similar. So we shifted our strategy to focus on the right pages, knowing that as pages got much more niche Google would still index them for very specific terms. With our focus on harder/broader terms, we were able to craft what we wanted for more competitive terms and also, like you, spend time focusing on things like rich snippets.
Are you doing any A/B testing, is that how you're changing out colors and such? That's been really interesting for us, same with changing the call to action wording.