"Is the threat of "burn-in" that great?"
"I thought that "burn-in" was all but handled on newer plasmas."
Yes, except for user stupidness. The scepticism behind your questions already puts you way ahead of a lot of posts in this thread ...
"Am I missing something?"
Nothing, unless you want to miss dozens of pages, obsessiveness, and ever more painful dancing on a pinhead.
"I will use it ... Will 'burn-in' be something I will have to constantly worry about?"
Nope. Use the energy to worry about something of equal concern. Like the type of soap in your dishwasher.
"list of guidelines to my family."
My suggestions ... see Post #628.
And I am serious about this - use common sense for the first couple of weeks and then forget it.