Frankly the Colts were at their best to START the game, as in when the rust should have been there. And I'm not sure how playing the week before helped the Chargers with Gates hurt and then LT and Rivers added to that list.
I mean the Colts rested the starters the final week of the pre-season. Then they pounded the snot out of the Saints.
"Rust" is intangible, it's impossible to be sure if it's helped or hurt to play. Only one aspect is certain, you don't get injured if you don't play. Again, just ask LT or Rivers.