I myself play at Noble usually and by the ti,e the really interesting weapons come into play I usually upgrade all my experienced older units. I define experienced as having 10-17 experience points at least. I find it a 'waste' to disband these units instead of upgrading. Unfortunately the amount of experienced units tends to be high in the later game, and I don't consider myself a warmonger. Upgrading is pretty expensive then. I.e., try upgrading 24 bombers to stealth bombers or upgrading 40 cannons to artillery. You're instant broke :(. Now I'm curious if you find that a fact too.

And please, don't give answers like 'wait until you play ...-level' ;).

I usually don't upgrade units as it costs too much but it probably isn't meant for upgrading a whole army. Out of date units should be disbanded as the upgrade cost will be enough to rush more newer modern units (with lots of promotions too if you have barracks, vassalage, theocracy etc).

I usually don't upgrade units as it costs too much but it probably isn't meant for upgrading a whole army. Out of date units should be disbanded as the upgrade cost will be enough to rush more newer modern units (with lots of promotions too if you have barracks, vassalage, theocracy etc).
Vassalage and Theocracy are a no-no in the later game is my experience (I'm talking about Mech Inf. era).

I tend to leave units obsolete until I need it, and then upgrade in one shot. Works best if you are preparing for a war.

Shift most city production to whatever units you will be needing that you may be lacking. Lower science by 10%-20% for 20 turns (or however long you will be pumping troops) and collect all the units you plan on upgrading to your launch points. At the end of your pump, upgrade all units with the gold you have collected. Declare war the next turn and roll over the surprised opponent. :)

Works best if you have a mid/late game UU. In this case, you would start the gold pump 20 or so turns before getting the necessary tech at your reduced science rate. I find this strategy particularly pleasant with the English Redcoats. Even if your enemy has managed to develop riflemen and cavalry, the sudden appearance of 100+ Redcoats will simply mow down his troops.

the appearance of 100+ any unit will mow down your enemy.

ok I have an idea for upgrading units. How about a higher support cost and then your troops are allways modern. Like in real life.

As I said before in my own post about this subject, the upgrading costs are too high at EVERY time, late like early, the cost should be reduced.

no i think its just right, maybe you just need to earn more money

I like how it is now. It adds some nice realism that you need to spend a few turns at 0% research to fund a big troops upgrade. Just look at the US now... we're researching Scientific Method at 0% and pouring all our money into the Iraq war :).