They already had the actors, sets, costumes. How much extra would it have cost to sit Gandalf down and have him read some poems and crap on set during lunch? Or improv some Bombadil on a green screen so the banshee and barrow could be filled in later.

I'm sure they knew many of the deleted/director cut scenes were never going to be seen in theater before they filmed them so I feel like there's a lot more they could have done with the intention of it only appearing in the 50 hour paint-drying release.