General relativity has several complications in regards to inertial frames, which I'm ignoring here because I think there's a more fundamental misunderstanding about special relativity and FTL going on here.
Now using Special Relativity, we could devise a frame of reference wherein the observer would see the Star blow up before we ever left planet Earth. Wouldn't that violate causality...?
No, it would not. The fact that you could devise such a frame is completely irrelevant to whether or not causality is violated. What's important is that nothing ever sends a signal to its own causal past, i.e. within or along its past light cone.
In general, an FTL signal of a fixed speed does not violate causality. To actually send something into your past light cone, you need FTL signals of at least two speeds in some particular inertial frame. That in some other frame you've sent a signal into the (coordinate) past doesn't matter. If you only ever use one particular FTL speed in one particular frame, no causal violations will occur.
Although physically restricting FTL to a single speed (again, in some particular inertial frame) would preserve causality, it would violate the principle of relativity instead, since there will be a unique, distinguished frame in which the signaling is instantaneous.
As for warp drives, we can take that as indication that a single warp bubble might or might not violate causality (depends on the geometry), but unrestricted ability to construct warp bubbles will surely enable us to violate it. This we can add to the many issues of constructing a warp drive.