Hey, I've only been playing Glest for three days, so I might be wrong here, but I find the game speed is at too slow a pace in the late game.
What I recommend is this - make the basic unit that give you food - pigs, magic source, etc. - provide you with half the food they do. This means early game, you need to use extra gold to get the same amount of units.
Then, make all units cost less gold. This is borrowing an idea from warcraft - the way it ends up working is that in the early game, it takes you an age to build up a small army of twenty units or so. But later, you can play a faster paced game, and enjoy more glorious, large scale battles.
Just an idea, tell me what you think.