I just ran into a perfect use case where the <podcast:guid> just fixes the problem in a way that nothing else does. I should probably write that up into a blog post and begin some broader explanation of why <podcast:guid> is so important.
I can see a Podcasting 2.0 STORE EMPIRE now... full of t-shirts that say:
"GUID is my Co-Pilot"
"You just got to stick it in there!"
"Podcasting is Audio Only"
"Meat Shake Equializer"
and of course...
"Money Printer Go Brrrrrr!!"