Do I understand correctly: The options listed in the section "Mobile Player Options" are the ONLY options supported by the mobile player?
Essentially, yes. There are a few other options that the Mobile Player supports (such as title and showOpenButton) but the Mobile Player does not support the majority of configuration options (such as audio, auto play, image scaling, etc.) which are available to the Flash Player only.
What about Juicebox - would changing vom SimpleViewer-Pro to Juicebox-Pro increase the customization options for use on mobile devices?
Yes. Juicebox (being an HTML 5 image viewer rather than a Flash image viewer) is much more configurable for use on mobile devices. Please see the Juicebox - Config Options page for a full list of Juicebox configuration options. Certain options are listed as Large Screen Mode options only (and, by default will not be used in Small Screen Mode) but you can force Juicebox to display your gallery in Large Screen Mode on all devices and in all browsers by setting screenMode="LARGE" if you wish.
For more information about how Juicebox adapts to different devices and screen sizes, please see this web page.
If yes, is a "cross-upgrade" possible, and how much would it be?
For more information about the difference between SimpleViewer and Juicebox, please see this SimpleViewer news article.
There are instructions in the link above for SimpleViewer-Pro users to receive a discount off the price of Juicebox.
And is it possible to migrate SimpleViewer galleries to Juicebox galleries?
Yes. Please see here for details.
SimpleViewer Support Team