I have thought about this a bit and I think the issue is that a wormhole will not prevent a timetraveling paradox if it in fact is merely a shortcut through the same 3 dimensional spacetime fabric that you would be travelling thru the more circuitous "straight line method" It would be possible for a photon to travel through one end of the worm hole emerging from the other before it left and having enough time to make it back to the entry portal and repeat the journey this time arriving even father in the past and heading back to the entry hole this time with its original self as a traveling companion... this process would repeat as an infinity loop creating a UV Catastrophe of sorts in infinite feedback and the only resolution I can think of is the instantaneously building intensity would destroy the wormhole.
It seems to me what you need to do in order to exceed C without violating causality would be to involve a higher spatial dimension. The only way i can sensibly explain this would be to simplify the picture by collapsing one of the dimension to make it observable from our perspective.
so back to Flatland.. I am sure you all know the tale of a 3 dimensional visitor peering down upon a 2 dimensional plane with 2 dimensional inhabitants. So just hypothetically lets say we remove one spatial dimension from the universe leaving 2 of space and 1 of time. Our observer from the "god's eye view" who previously was 4 dimensional (well 5 including time but were gonna leave that be for now) is now a 3 dimensional entity like you and me..
This being looks down upon the 2 dimensional universe and can see vast expanses of it.. and we are gonna get a step freakier and say that he can actually *see* time itself radiating thru the universe as it expands... yes I know.. but bear with me I am theorizing.
In effect he has access to a vast variety of reference frames from each point on the spacetime sheet.. he calibrates a clock at two distinct locations separated by lets say 10 light minutes on two separate worlds that are capable of observing each other thru telescopes or whatever means... we're gonna call this dude X btw
so anyway he picks up subject A from world 1 and places him over on world 2 next to subject B who sees him arrive and then picks up subject B on world 2 and places him next to subject C back on world 1. The trip each way only takes a few seconds from his perspective. They have traversed the distance *much* faster than the light/time radiating from their respective worlds which to the X appears as slowly spreading rings like ripples on a pond.. very slow ripples..
Ok so lets say you are on world 1 and look at a video feed of the clock on world 2. It reads 10 minutes prior to your clock since that is what time it said when that information left and headed your way. The same applies for world 2 observing a video feed of World 1's clock, it appears to be 10 minutes slow. Now a little less than 10 minutes later subject A appears on the video feed for world 2 as viewed by Subject C who has been having a conversation with Subject B. Subject A would have traveled far faster than light but he would not have actually traveled in time. He would appear on the feed at time 0 plus a few seconds according to the the video feed. In fact if X picked subject A back up and returned him to world one after a few minutes then subject A could watch himself appear and then disappear on the monitor.
Now if we reinflate the universe back to the normal amount of dimensions this leaves us with a 4 dimensional X who could pluck us out of our 3 dimensional space and put us somewhere else at apparent superluminal velocities but it would not violate causality.
I know I am missing something here and I have a sneaking suspicion it relates to an assumed absolute time reference frame but I can't put my finger on it... I am just going with an event either has occured yet or it has not regardless if the information regarding that event has had time to reach you. Basically if we were to use this method to travel to a galaxy a billion light years away we would arrive at whatever that galaxy looks like a billion years into the future from our starting reference point because that what it actually is.. it just looks younger due to the time delay in the information leaving us..
basically because X calibrated the clocks to his outside perspective.. if for instance world 1 were to observe the video feed and calibrate their own clock to match the time on world 2 then even an instantaneous trip through the 5 dimension would deposit them on the destination world 10 minutes in the apparent "future"
I hope that makes sense.. it's the best stab I can take at it.