That depends on the strength of his economy.
Either he needs money and should therefore pick an Idea that boosts trade, production or tax efficiency, or viceroys. Or he has enough money to spend, and keeping Colonial Ventures is good, because he can colonise more provinces each year, have the random occasional new province settled by Venture colonists, and will cover faster the provinces his explorers discover - reducing the risk of map spread, and reducing the time where he'll actually need to keep QFTNW as a necessary idea.
(and also @ Barsroom)
For some reason I though he didn't have Colonial Ventures, despite the fact that I looked at the last empire round up before I made that post to double check.
So, to answer the original question I was responding to: he has every colonial idea.
On to the deeper strtageic debate about NI's.
He currently has military drill, divine supremacy, church attendance duty, colonial ventures, national trade policy, QFTNW, Cabinet, and Land of Oppurtunity.
I honestly feel as though, in general terms, he could replace Military Drill, Divine Supremacy, and Colonial Ventures.
-Colonial Ventures:
Map spread seems to be manageable so far, and the random colonies gained by random event and the extra colony per year I don't think are worth it. I seriously doubt this game will be decided on a lack of colonists. Colonial Ventures means an extra 120 colonists over the roughly 120 years left in the game. I'm not sure what his colonist income per year is, but considering he (I think) borders a few hordes, is Catholic, and has to have a few coastal CoTs by now I wouldn't be surprised if it was 2 or more a year. Call that 240 some colonization attempts. Asuming he preps the area by clearing it of natives first, his success rate is (conservatively) around 70%, call it 160. I'm not sure how many provinces are currently left uncolonized, but I think 160 should be enough, since all he has to do is succeed once and let it grow on its own.
-Divine Supremacy I kind of already covered, but just to review: at this point the primary benefit it provides is .5 missionaries per year. The event chains it enables or blocs are a mixed bag, so it evens out. its primary strategic purpose (war against heathens) has played out.
-Military Drill
His army is bigger, tends to be more technology advanced, and is better led than anyone. I'm not sure an extra morale point is that big a deal. Primary benefit is for assaults on tough provinces.
In my view, there are two obvious contenders for the "what he should replace it with?" question: Smithian Economics & Beureucracy
His economy is really, really strong, but he could make it stronger. Both of these represent a flat percentage bonus, which would work particularly well for a large empire such as his. The extra money thereby produced would allow a greater number of colonies to be maintained in the first place, and might enable him to have enough spare money to finally have a modern navy, not to mention the general srtategic flexibility that richer economy lends him. Smithian Economics, with its boost on production, would magnify the income effect he gains from the higher demand of some goods which occurs during a war. In short, I tend to feel that the general currency of "more money" is more powerful than the "saved" currency of being able to colonize faster, at a reduced price, or for free, or any similar "specific" benefit once its fundamental strategic purpose has been served, which is arguably the case. Colonial Ventures allows his to do more colonizing, but more money lets him do more of whatever he happens to need most at the moment.
I'd definitely drop Divine Supremacy and adopt Smithian Economics in its place. The debate over which is less needed, Military Drill or Colonial Ventures, is actually a bit of a toss up to me. I'd have to be experienced this game first hand and get a sense of what my actual problems were.
Of course, he's doing fine as is, from all appearances, his economy already dominates, so to a cetrain extent this represents Min-Maxing on my part.
