There are separate software versions for the old Rev113 Cruz system board and the newer Rev64 Binky board which you have (cpu hardware revision). Files for the Rev64 are in thread http://www.robotreviews.com/chat/viewtopic.php?p=134696#p134696
There is not much additional beyond v3.1 which added the "corner clever" maneuver for better cleaning in corners.
v3.4 is the last update for XV models; no updates have been made to Botvac
's without WiFi. Like driver software in PC's, there is little need to update unless there is a specific problem to address. Flashing the firmware entails risks of errors damaging the system irrevocably. Flashing is performed by the robot itself, which has to be intact to perform any such operation -- catch 22 so to speak.
The WiFi models can use more frequent updates just for the complications of WiFi itself, tying the robot to a separate technology with changes over time in standards and methods, not to mention incomplete software to begin with.