My first choice for games that aren't fundamentally broken is to just get an errata-corrected edition out there. So, like @TheophilusCarter, I would find that most welcome!
If there is still budget available, any improvements to layout, editing & organization would be great. If there's room for some serious changes, I like the idea of presenting the system as stripped down as possible in the first few chapters. Maybe make that Part I, with the listables (monsters, spells, equipment, etc.) in Part II, and then Part III gives the options. Or make Part III the Companion.
Finally, yes, bring it up to date, adding stuff from RQG, etc.