1.

In full honesty, I would pay for the service 5 Euros. Now, the reason is the insights it gives me are well, not really too accurate, as the given ratings (SEO should stay consistent) changes. I got 72 once, and 65 on the same website. That kinda kills the trust. Also, the amount of features that the service offers is not enough for me to give $30USD, a month. Looking at your service, I could imagine a free limited tier (eg. 5 audits / per month), and a pro tier of $5-$10 with unlimited audits. Always charge at first, but I mean, it does have to be realistic, $30 for a clean UI, Dashboard, and a simple Audit, is not worth the $30. Also, a few false positives aswell, it told me to add meta description, even though I already added it to the index page.

2.

Previews for color changes. Eg, how the color contrast would be improved if you did take the styling change. Would display results, and motivate change. Scan files, not just RAW HTML. Like, upload a folder, let your service view it, and rate it (would be good for devs coding static sites).