This works well in sims, like Tropico. The economic model in most sims tends to be rather different than that in RTS games.
In sims, people come to your town if conditions are right, and fill the available jobs. Often you can't even control individual villagers. The 'work experience' factor is an incentive to keep your current villagers happy, rather than constantly replace them with new ones. This stops you from doing something extremely unpopular (but highly profitable) for a while and then return to the previous situation as if nothing had happened.
In RTS games, you usually pay for each villager, you don't need any additional incentive to make sure you don't lose them. There is some micro (in some games: a lot of micro) needed to put each individual to work. Adding experience seems like it would add too much micro to handling the economy.Maybe it could work in an RTS with a sim-like economy, but AoM seems to have a rather traditional RTS economy.
It's still an interesting idea though