Ever worked for an "idea guy" CEO?
New idea every day/week/weekend.
To me, idea guys is a symptom of insufficient skin in the game. When the CEO has skin in the game, time is valuable, and they really quick start focusing on execution and the value of time.
Terrifying.
After each "new" idea, spend about half an hour working on the idea. Best to do this on paper and target producing some good looking notes. Then file it away close at hand. If the "idea guy" ever follows up and asks you about their idea, pull out your notes and say "ahh yes, I've been working on that and I have a few things to discuss with you." You now appear as a hard working and enthusiastic underling. For the majority of cases where they never follow up, you have limited your wasted effort.