First of all, I am coming for a complete Noob perspective so I don't know much about how difficult it would be to change certain things...but if I had to pick 2 things I would like to see changed is like search function like you mentioned. I have such a hard time finding quality posts to comment on. I like to search through the new section because of I like to support Plankton like myself but I have to wade though thousands of posts to find that hidden gem.
I think that all the posts from Zappl, Dmania, etc should be seperated in a different layout both in the search and in your personal Steemit page. I really have avoided using Zappl and Steepshot because I don't want them showing up right over the blog posts that I took hours to write (it takes me hours because I have never written content before)
The other thing that I think would help the promotion of Steemit is maybe an affiliate sign up bonus (even if the incentive was a small amount of SP delegation) to encourage users to bring their friends onto Steemit.
I am actually working on a blog post about this from a noob perspective today and I realized that the future success of Steemit is dependent on the health of the crypto market as a whole. Since there is such a steep learning curve with Steemit people will need to learn the basics of buying crypto before they can even think of starting here. It would just be too overwhelming otherwise. I am however extremely hopeful about the future of Steemit :)