I'm sorry but I can't recommend this. It's clearly a thought out idea, and one that certainly seems to strive to cut down on false advertising with the in-game trading system, which is a good thing. There's a couple issues I have with the suggestion as it stands however.
It is on too small of a scale, too focused. Okay, this tells me that the engineer that I'm looking to buy is a +10 when he's advertised as a +12, perfect it fulfilled its purpose. But what does this provide when I want to know the base repair of the same engineer? What if I'm looking for USN gunners and want to know the base and what's available has been bounced back and forth between Acc and Rel?
Additionally, as you know from your own experience, there is much more to a sailor than just their base stats. This won't address classing. Fighter pilots and the preference of some players in delay classing them for crew growth is the first thing that comes to mind. For some looking to buy, there is dramatic difference in sailors desirablility based on when they were classed. Trying to sell UK AA gunners, already a hard sell, would be considerably more difficult if they were classed on time.
My final thought and issue is that the idea would be on the in-game trade board panel. So if I've got a sailor sitting around in my harbor for a while and I figure it's time to sell him, but I don't know his base growth for his primary ability (already determined that's the only stat that is displayed on this sprite). I have to enter my account code to enter the in-game trade system and then filter through to his specific class, write down or memorize what the base growth is based on what he has since the trade window is on top of everything, then close out of the trade system window before going through the actual motions of preparing my sailor to sell.
Please don't feel this is just some going out of my way to flame you as I know there are plenty of issues between yourself and a number of people on the forum. The concept and intent behind the suggestion are great, with tweaking it could work. Don't take this as a shameless plug but I also came up with a suggestion that serves a similar goal, you're welcome to visit that suggestion and pick it apart. Forum thread 'Sailor History Window'