Upgrading units

[Andorim]

Is it a good use of gold to upgrade military units? If so, when?

Would it be better to delete the old warriors and axemen as you build new infantry and tanks? During the middle and end-game, I have this hang up about getting all of my units upgraded to modern standards. I am not sure that this is the best use of my resources.

Do you upgrade your units? If so, which units, and when?

[Eggolas]

I upgrade:

City Raider troops to appropriate gunpowder era troops such as Grenadiers, Riflemen or Infantry and especially Redcoats.

Disband troops that are really obsolete. Warriors and archers when I have Riflemen for example. As I build new units, the older ones get disbanded. It costs too much to upgrade the very old units.

[Andrei_V]

I upgrade:

- Veteran units
- Melee units with City Raider to Gunpowder units (such as Rifles, they cannot get CR otherwise)
- Cats to Cannons when in the middle of a military campaign and no time to wait till new Cannons are produced
- Likewise, the Navy, Galleys -> Galleons -> Transports
- An occasional Longbow to Rifleman when the city is suddently under attack, and I did not bother of course with upgrading garrisons. I believe it is a lot cheaper to keep those 30 or 40 Longbows and some cash to upgrade one or two of them in case of emergency, than to produce 30 or 40 replacement Riflemen.

[Sisiutil]

I also usually only upgrade to preserve valuable promotions (like City Raider for gunpowder units, as above), or if under attack.

The cities at the core of my empire, which are non-coastal and surrounded by other cities, often end the game protected by the same Warrior and Archer that they started with.

[Silver Marmot]

I upgrade:

- Units with City Raider. This promotion is great for attacking cities, but is not available for gunpowder units. Gunpowder units are great with this promotion.

- Garrisoned units when I need to defend a city in the next couple turns (assuming I can't hold the city otherwise).

Other than that, I find it preferrable to build new units and use the gold I saved to run my research higher.

[Bushface]

I wholly agree with Silver Marmot and Sisiutil. Many's the time my capital's garrison has been a 5000-year-old Warrior, his erstwhile Archer companion having been moved out a little to keep another city happy. Regular upgrading is hideously expensive.
However, I sometimes upgrade a few bombers to Stealths if that will help me finish off an opponent quicker.