haven't lost interest in Thirteen, since she was off-screen for the season, so I might check into the last few to a) see what is going on with her and b) to see how low the show sinks

Thirteen's arc isn't bad, a little cliche in places perhaps, but
actually sort of satisfying in others. The Chase/Thirteen sections of the second to last episode are by far the best.

The Glee finale had a nice snap to it, but it's far beyond my ability to suspend disbelief to believe that they could write original songs in a day and do well on stage.

Eh...Glee jumped past my suspension of disbelief a long time ago - it's almost too satirical to be taken remotely seriously.
(The kids are being played by adults.) But I agree, it has gotten very silly this season, what with Sue's insane antics,
and the Holly guest shots.