I'd also like to disable the Player main screen display of Play Doctor -- It confuses my users. Everything they do is based on carefully constructed playlists, reinforced by a custom Play display, yet before/after Play they can't avoid the prominent Player main screen area. Confused, users sometimes click Play Doctor, yielding unexpected and inappropriate results for our situation -- and complaints that something is "wrong".
Given the massive customizing possibilities of most of MC (notably, customizable Play displays/visualizations and the long list of Features that can be enabled/disabled), it seems really odd to force Play Doctor (or any particular MC tool) to the Player foreground for all users. It's an odd default for a product that offers so much versatility (and quite misleading when displayed in a video- or photo-centric MC library).
I'd much prefer configurable MC home and Player default screens, including the option to show simple HTML pages of custom instructions for our specific use of MC.