Rapture Pro does have some features that make the upgrade worth it.
The ability to search for patches
The ability to have favourites
It will reuse waves that have been loaded from previous patches (if required), rather than reloading them
Having all your patches from Rapture, Dimension Pro, Rapture Session in one synth
Note: I would not deem Rapture Pro a replacement for Zeta+2 - for instance, Zeta+2 supports polyphonic aftertouch events (each note of a chord can an independent intensity of effect) whereas Rapture Pro treats polyphonic aftertouch events as channel aftertouch events (The effect operates on all notes of a given chord).
These are a few things
What I would suggest id try the demo. It's really an individual thing.