I picked up a well worn second issue Colt Agent over the weekend.

Thinking of sending it back to Colt for a factory refinish - I know there are those that say keep it as it is and that you will never make your $ back on any refinished firearm but I am not looking to sell it and honestly based on the price I paid and what they are going for on Gunbroker if I did I think I could still break even.

Now I just have to decide if I want to stick with blue or possibly go nickel.   Hmmmm.....

Shoot it, clean it, oil it, and leave it as is.

Sorry to be late here, other things going on.

Colt will NOT refinish any aluminum frame revolver.
There is too high a chance the frame will crack if an attempt is made to remove the barrel.

Ford's refinishing apparently does do re-anodizing of aluminum Colt's but I'm not sure what they do about the crack risk.
I suspect it's at the customers risk.

Other options are:
Hard chrome.  
This may be possible without removing the barrel.  Most platers will not hard chrome aluminum due to a high risk of damage to the plating if the gun is dented and the soft aluminum causes cracks and even a flake off the plating.
Usually they plate the steel parts and just bead blast the aluminum, but that won't work on a revolver without barrel removal.

Nickel.
You can go with bright nickel or satin electroless nickel.
Bright nickel was originally offered by Colt.  You might contact Colt and ask about bright nickel as a factory refinish.

A paint-type gun coating,
Most gun refinishers offer a variety of epoxy based coatings that can be very durable.  Today the most durable appears to be Cerakoat.

With the hazards previously noted, I would first consider just enjoying it. Maybe some cold blue if you really feel the need.

Second choice would be Cerakote, but I would hesitate on that one because the pistol's value would definitely take a hit.

With the potential for damage making the pistol valueless, and worse, taking an old Agent example out of existence forever, one of those two choices would be about it for me.

I can't see any rust in the picture, just loss of finish, so just keeping it clean and oiled, and stored in a VCI bag when not in use, would maintain it's present condition for the grandkids.

Oh, and by the way, if the picture is accurate at all, it really is in pretty dam nice condition. Too many people want "new" looking old handguns, but these pistols are tools that were made to serve a useful purpose.
Take a look into your toolbox in the garage, and if all your tools look "new", then you aren't using them for what you bought them for. ;)
The husband of a friend of my wife's died recently (at about 80yo). He was a retired NYPD detective. He showed me his nickel Agent that he carried for most of his carreer, and it looked like hell. Some flaking, been dropped... a REAL "working" pistol.
I would have given his wife anything to get it but it was one of those things that disappeared right after he died. No one knows where it ended up.
If I could have bought it, I assure you that I wouldn't have touched it in any way other than to shoot it. The wear on a lot of older guns isn't wear, it's history, and while I like new looking guns like anyone else, I also enjoy the history of some of the used ones I've bought over the years.