He only signed Manning? First of all, I like how Grigson gets 4 votes for drafting Luck. Manning was a free agent. He could have played wherever he wanted. Luck had no choice.
And then also, all in all, the Broncos have drafted OK under Elway.
You could also look at other FA acquisitions that have been solid. Holiday, the DT last year (that Im blanking on) who went to the Saints, McGahee, Adams.