Problem with wxBasic is its age. The last stable version was released five years ago, and the latest "bleeding edge" hasn't changed since early 2006. Not a whole lot you can do with that, unless you like the idea of going back to 2.4 or earlier.
Kind of a slow reply, sorry.
I'm not sure if the age thing is really that big of a deal. wxWidgets is very feature complete and has been for awhile. It's at least more complete than MaxGUI, so even if it did mean going back to wx 2.4 I think that'd be an improvement. Then you'd have a base to start working on support for newer versions of the library or just fork the think and do a BMax only version of it.
If I were going to create a GUI for a BASIC compiler, I'm pretty sure it'd be with wxWidgets. But it is a lot of work, no argument there.