I completely agree with you, we cannot expect aliens to interpret pictures, movies, sound and text the way we do. Even if they would be able to see the same spectrum as us, it remains doubtful if those images will mean anything to them at first glance. However, the point here is to convey information. While we can look at a picture at all wavelengths, it is only in the visible spectrum that information on this picture (patterns and variations) start to appear (at other wavelengths, its blank). An analogy would be satellites using SARs to pierce the cloud cover of Venus and image its surface.   There is little information in the visible spectrum but lots outside of it. If the information is encoded in a digital form (eg: RGB) rather than displayed using our technology, then they will interpret it in colors they can see as this encoding is not relative to a specific spectrum. Still, they should be able to figure out what king of colors we meant to encode in the first place by looking at the probes themselves and the markings on them. I think that the aliens will be able to make sense of this information easily. Regardless, I completely agree with you. It will take them years to analyze what we have sent them and make sense of it (ie: convert it to something they can relate to), but if they feel as lonely as us, then I trust that they will invest the resources and time.