yes.  i agree.  What I'm also interested is in the 'refitted' unit retaining some, if not all its battle earned experience.

I think this is a bad idea. Fortress training abilities are already so good, they don't need any more distribution to extra units. This will favor the player over the AI, and I think that would hurt the game at this point. 

Second, using troops who have weaknesses to offset their experience gives them more flavor, from where I stand. Isn't it a good gameplay choice- the quick, better trained hotshots who will die with one hit, or the clumsy old guard who can take an unnatural beating? Both cost wages, where to best keep putting your money?

In a related thought, upgrading unit size should have a level penalty- that newcoming sixth troop didn't slay any dragons, the five veterans before him did. 

I am no expert either, but just because it was easy in Civ2 doesn't mean it's easy to make happen here - especially now that so much code is written, changing one cog here can potentially cause cascading unintended errors elsewhere. 

My real reason against it is, I think it's more a gameplay negative than positive. Despite the joy of total control in games, hard choices between two negatives is (almost) always more interesting that just getting one positive. 

Agree with the OP. The mechanism should favour keeping veteran troops, which makes keeping them more important. 

AI difficulties notwithstanding.