It was obviously something that was removed from Glest, in an early V3, but not from the Unit's desc string. GAE still has the 1.2 multiplier per level (by 'default' of course, our levels are mod-able).
Thanks a lot, ... but I must admit, I can't understand, why such a basic function - which is included in the majority of strategy games - is removed. Unit upgrading gives several additional possibilities for strategies... You do not have to simply build a mass of units (what is - and this is
not only my personal opinion - stupid and boring...), but can concentrate on 'train' several units to stronger 'specialists' in order to save lots of resources (a unit, which lives a long live is much more convenient than a herd of - greenhorn/disposable - units).
So obviously the GAE team concentrates more on strategy than simply on BOOM-BANG...

To be serious, once again: Why does Mega Glest not support unit upgrading? There is hardly a problem in gameplay, if this works... and for interjections concerning 'balancing'... you will
never reach a balanced game, as long as there are different faction involved. Upgrades also can be involved in the process of balancing... and if persons (humans...) are overcharged with this balancing, there is still the possibility to arrange PC's playing against each other and changing relevant parameters using - for example - some kind of KI (like evolution strategy, which is everything than complicating in this special case). My last statement might sound utopian to some readers, but... imagine a faction. Every unit is defined using parameters, which altogether form a 'genom' (per unit). Permanently early dying units are too weak - their parameters need more changes. Which changes are need? Well, if - after a genom change - these units die even earlier, the change was silly. This genom dies, without a chance for reproduction, whereas other become stronger (= live longer, higher rate of reproduction)... and so on.
There is no limit in possibilities, but - of course - a few machines should play the game several times with different factions (as with as many factions simultaneously as possible)... of course these games did not need to be 'visual' (graphic completely disabled) - except the first few games, which need to be visual for a first check.
Of course this will cause once again several people throw their hands up in horror or shaking their heads, but ... there's no such thing as a free lunch. Balancing either is one aspect of a game or it is of vitally importance.
A suggestion:
Why don't you make en-/disabling unit upgrading a part of the configuration (as a part of the games options,for example...)?