Seriously, there's a pointing finger with "Sparks over this way" - that's your tl;dr shortcut right there. I like this site a whole lot.
Nice cartoon work, btw - where did that come from?
On the feed page, I think you could reduce the text on the sidebar. I dont care about the welcome message, if I'm registered why do you explain me the website again I should already had understand what Sparkmuse is about. I would delete that paragraph and replace it only by the "Create Spark" button (make it big and colorful, I didnt saw it the first time I saw this page)
You can also reduce the "We want feedback" block maybe you can install uservoice or something.
On the spark page the solution appear 2 times at the top of the page and on the sidebar. Why ? Maybe you should put the question and the solution at the top of the page like Quora/Stack Overflow or other discussions board.
Again it's only my PoV. You made a great job .
I'd not say 'improve' - call it expand :-)
Being verbose has its own advantages too. One that I can immediately point out is from SEO perspective.
As most know, one thing the SE crawlers love the most (besides links) is content. Content rich (i.e. verbose) pages are usually good organic traffic magnets. (On the flip side, they can deter many human visitors! The Catch 22 is, common webmaster guidelines say 'optimize for human visitors'.)
Put yourself in the shoes of someone who doesn't care about you at all. Explain the unique benefits that that person can access right now. Appeal to their selfishness. Focus specifically on things that Sparkmuse enables (right now) that cannot also be said about alternative sites, such as Hacker News. Trim everything else away.
I just registered on your site, I love the idea and the design. I was also afraid that I would land on an empty site, but there is already lots of idea to read and discuss about.
One little think that I think you can improve. You seem to love to write :) and I guess talk . We feel that on your website there is a looooot to read maybe to much.I find so much text overwhelming maybe you could reduce or delete some of it. My 2 cents...
Good luck on your project and congratulations !