The newest software update is supposed to be the latest and greatest.
It should include any prior additions/enhancements.
But, be aware that the updates sometimes have bugs.
What used to work in a prior update may not work as well in a newer update.
This is just a fact of life when hardware is changing and software is being refined.
In my humble opinion, you are better off having the newest update.
If you have a problem with your unit and you call Humminbird, the first thing they will ask you is if you are running the newest update, and if you are not, they will recommend you installing it.
If you have doubts and your unit is running well, then you could hold off and check some of the forums for potential problems with the update before installing it.
Good Luck.