A man can dream. Damnit, you're loaded you can do whatever you want.
I think the store would be a partial risk. Obviously while the site is quite popular it runs un-noticed in comparison to shit like Ebaums etc. Do you think the general public would enjoy Newgrounds nostalgia if they haven't heard of it.
Obviously the designs would sell on their own, and from there you would get alot more traffic for the site.
But right now you have alot of Newgrounds stuff to sell! User DVD's, clothing, stickers, misc... it would be a risk, but it could pay off.
Knights
I say go for it man, most of the greatest buisinesses and inventions in history were made on a 50-50 chance hell even Newgrounds must had some risk involved in creating it.