I think a quality post is something that incorperates the intrests of the majority. That's the thing about this new realm of social media......it must take into account, social interests, meaning, the interest of the whole community....developers included.

Steem is a merger of cryptocurrency with social media. Both interest are important. Its cool to "just be yourself" but its also cool to be "mindful of others". Its cool to make interesting art but its also cool to make profits from business.

For the business crowd a quality post is a post that adds value to the steemblockchain. Text or "long posts" do that. This may change in the future as the steem formula improves upon itself but in its current stage, text, alongside interesting journalism is value for the business folks. Financial investors appreciate news.

For the artistic crowd quality content is a much more coloful consideration. It is true that artistic content will always drive value the furthest as it is often much more attractive then text an numbers on a page but art must consider business as business has considered art. Steem is a business that created a space for art.....therefore, those in the art world should be considerate of the interest of those in the business world.

All these thing being said i think a quality post on steem is one that incorperates the interest of both parties......interesting well written content (that has some body to it) as well as artwork an so forth that represent creative self expression.

Hope this helps.