With the exception of Grodd, and perhaps Mirror Master, I don't see much need for cutting edge special effects work. Ice, fire, and weather certainly have been used before.
I'd be surprised if the first Flash movie involves much more than superspeed. The general pattern seems to be to start relatively grounded and expand in scope in the sequels. Even if Flash breaks the mold in that regard, I'd be surprised if the first movie involves dimension hopping, time travel, vibrating through solid matter, hidden intelligent ape cities, potential city-wide/planet-wide destruction, etc. all in one movie. I expect that those ideas will be doled out more frugally.