There is a caveat to the legality of classified materials, usually you must have been "entrusted with or having lawful possession or control of". Which alludes to the fact that you would first have to have been read in, or taken the material that you knew was classified.
There is also a "requirement" to "knowingly" cause harm. I put these in quotes because the wording and the enforcement of that requirement has been in flux and selective. Also relevant is that gross negligence would also meet the requirement.
I guess a creative prosecutor could challenge that visiting wikileaks would be knowingly removing the material from the server, but it would probably be beyond difficult to meet all of the guidelines for prosecution.
That being said. If you do currently hold a clearance, visiting Wikileaks is a violation of your NDA/ReadIn, Employment Agreement, and the UCMJ for service members.