D7 conditional field option?
Against my better judgement, I've used Conditional Fields to control field display. I'll post back here if I have any issues.

To anyone who arrives at this answer from Google, I made at my decision after looking at the module's usage stats, which paints it almost at parity with the stable D6 version:



It's worth checking out http://drupal.org/node/1551504, which is intended to spur a D7 stable release (The author looks a bit overwhelmed by it all, truth to be told.). I've closed any similar questions and pointed them to that, which seems to have the most traffic.

That all said, it's kinda hard to contribute to a project when the maintainer is MIA...