Oops, I forgot that I was going to provide a list of inaccuracies in the text descriptions. I will look for them in the new version when I find some time...
As for the scout upgrades, just a bit better combat strength would suffice for me, so the upgraded version can be used in combat in later phases of the game, when you don't need them for exploration that much. The promotions for recon units are quite good, so an experienced scout upgraded to a stronger version will be useful for combat recon and hunting enemy units in remote areas. Of course you can give them some special abilities too, for example the ability to traverse deep ocean while embarked before the other units can do it.
As for the scout upgrades, just a bit better combat strength would suffice for me, so the upgraded version can be used in combat in later phases of the game, when you don't need them for exploration that much. The promotions for recon units are quite good, so an experienced scout upgraded to a stronger version will be useful for combat recon and hunting enemy units in remote areas. Of course you can give them some special abilities too, for example the ability to traverse deep ocean while embarked before the other units can do it.