Interestin' thought.
I've not played American Conquest, so I can't really make much of a comment there, but Europa Universalis is a truly amazing game. In fact, all of Paradox's games are bloody fantastic, but I digress...
I'd personally say that something to learn would be from Akella, and POTC, with the element of character `skill-building`. Aye, its nice to know that at the age of 18 I'm a master fencer, but its nay that believable when all I've done so far is beat the living hell out of a Captain. <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/wink.gif" style="vertical-align:middle" emoid="

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Personally, I'm not sure that EU2 would be a good path to walk down, purely because it was designed with the player acting as controller of a country, rather than Captain of a ship. If you want to have the political minefields, adaptations and events of EU2, they'd have to be in the background and under player's influence rather than player's control.
I can see the benefit, say, of having England have a political 'policy' with regard to the Caribbean. For example, if their immigrants and traders are unmolested, they might choose to put more focus on their colonies there...or, on the flip side, they might take away 'excess' military forces there. The player would not dictate England's policy, but could certain affect it...thing is, would it really add much to the game?
I don't think it would, in all honesty. IMO, Pirate games generally work well on a micro rather than a macro level. The focus should be on the personal, individual elements rather than the distant `nation-states`. Not least because a large number of the colonies would casually ignore laws from back home that didn't suit them.
In terms of ways to generally improve piratical series, I'd like to see a swing towards characterisation. For example, Pirates! always appoints you as the Captain. Barring montary concerns, your crew follows you utterly to the death, even if you're a `merchant-just`-`turned-pirate`. That sticks a little, for me. Sure, it makes the game very easy to get into, but I'd prefer there to be more realism in that sense.
For example, your First Mate might decide that, actually, he'd make a better Captain. Do you let it run as far as mutiny, or accept that you'll have to divide the plunder unevenly, or reach some kind of arrangement...or just keelhaul the blighter? Likewise, you might have a particularly corrupt governor whose sole presence allows you a safe haven that you desperately need...only when he is removed from office, the new governor might hate piracy and refuse to even see you, and order you attacked on sight.
Its a shame that the ships, too, don't attack you. I've sailed in front of pirates with virtually no crew, no cannon and vast sums of money from `treasure-huntin`'. Sure, maybe they didn't know that, but rumours spread, and any pirate worth his salt would surely have come over to have a look...
Likewise, after I'd `single-handedly` sank about 18 ships of the French Navy, plus 7 or 8 pirate hunters, about this kind of time you'd expect them to put together a small fleet to take me down...it just never really feels like you're truly in danger in Pirates! If you're outmatched, you simply don't bother with the fight.