I've been really enjoying the Gold Campaign, but one thing I would like to see in the final version is more "elite" units like the hypaspists and more reward units like the agrarians(sp?). I know Alexander employed a lot of elite formations, but I'm pretty sure Philip had Asthetairoi, which held similar status to hypaspist but fought like phalangite. Adding at least one type of elite phalangite would be cool, imo.

Yes I think so. As your empire grows, it becomes nicer to have an "elite unit" per army. I typically split the Companion Cavalry and the Hypapists up, bringing them together for special assaults on large cities.

Maybe as each faction is destroyed by you, you gain a special unit from them? Like if you destroy Sparta, you get the Spartan Elite Hoplites? And with Athens, a special naval unit, like a Greek Fire Trireme?

Thessaly should provide an elite cavalry unit, elite thessalian cavalry played a major role in both Philip and Alexander's armies. And all macedonian armies for that matter, till their last battle against the Romans.

As for units, don't know. What I was not so happy about was to find out Agrians don't level up anymore - understandable in context, but did not made me too happy.
Same with other units - totally removing levelling kind of restricts their usage. But not sure it would be good option to let them level up fully as natives, too.

I agree with the levelling comment. Totally removing levelling for allied units takes a small chunk of the fun out of the game. No one would say that leveling is overpowered, and while I appreciate that it means that your native units will always be stronger I'd like to be able to make all my units stronger. Even for just the fun of getting a new level.

If you wanted to make allied and merc units less powerful than the natives wouldn't doubling the XP requirements of each level make more sense? Or even just reducing the number of points the get per level?

This would also have the effect of representing a unit becoming a veteren rather than just being trained already at maximum effectiveness.

I agree to the idea of more special one off units, I personally don't know what they could be, however I am sure there are many historical units one could use.