Average to slightly above average player.

So far, great coach.

I agree. What makes so-called average players good to great coaches is that more than likely they didn't have all the physical skills of the game. They had to rely on the mental aspect of it, the repetiveness of doing the same exact fundamental things every day.

Incredibly "gifted" athletes usually do one of two things (so it seems):
a) fade out of baseball with a ton of "potential" because they never put in the work to become perfect in their mechanics and everything else and be consistent day-in, day-out --or--
b) they work hard and become great--what happens here, though, like with Michael Jordan, is that they don't understand how, if they are teaching someone the right way to do something and see this person working hard at it all the time, why this player isn't great. The usually get frustrated and thus don't seem to maximize the abilities of those they are teaching.

"Average" players, on the other hand, have a number of qualities: consistent work ethic, ability to be patient with superstars (as they may have had to do while playing), and an understanding of where the lesser-gifted athletes they are teaching are coming from, and recognizing their roles and how it would fit on a team.

These are generalities and are only my opinion. But they seem to work to me. Certainly, not every average player is a great coach (duh) and some great players could be great coaches.

I don't know how, though, "greats" like Maddux and Grace, who seem to have become great with technical skill and a great work ethic (from my limited view of baseball the past 10+ years, but I wouldn't be surprised if at least those two could do it. But who knows?

I'd like to see Ryno given a position as first base coach and infielders coach.  Sandberg played shortstop all through the minors, played third for a year, and then excelled at second.  He has always said he didn't have the most natural talent, but worked hard before every season and before every game to practice his fielding.  I think any player would respect that.  If you're going to put a fan favorite somewhere, it's going to be first base or bullpen coach.  

I think where you get into the most trouble with star players coming back as coaches is the hitting coach and the pitching coach.  No Fergies and Billies, please.  

Among former Cubs who weren't stars, one possibility is Gary Varsho for bench coach.  He was let go by the Phillies, and has talked about wanting to come back to Chicago.  

There's also a diversity side of the coaching staff.  If you hire a white, straightlaced, former catcher as manager, chances are he'll hire a couple of minority, fun-loving, former outfielders to the staff.  It helps for each player to have someone on the coaching staff to relate to, since a ball team is much like a family.  That's not to say there have to be clear ethnic, religious, or other divisions in teams, but that the coaching staff usually reflects the makeup of the team, for good reasons.  And, yes, at least one of them usually speaks Spanish.  

manages people exceptionally.

Coaches develop talent, players execute.  But managers can look at the team they have available, work with coaches and players, and make the best team possible WITH WHAT THEY HAVE (cough, Dusty!).  Without working together and having the managerial skills to motivate players to work together and to play on their weaknesses and strengths, a manager is Dusty
Baker.

Thus concludes my argument on why good baseball players do not necessarily make good managers.