Is there much of a point in gameplay terms to accepting marriage? Tried one game with a minimal feast, another with very expensive (relative to 2 months into the game) feast, no difference I could detect, and the news not all that useful.

Under what circumstances do you find it worthwhile? Should one maybe wait until he can afford a very lavish feast or something?

Once you've pretty much played the game through (got the baddassinest pirate dealt with, etc.), your wife gets kidnapped all the damn time. Gives you some generic missions to do once your fleet is kicking butt and your convoys and businesses are raking in cash.

As far as paying for the bigger wedding, not sure it makes a difference.

I don't think the size of the feast has any effect - it's a requirement, not something to give a bonus.
If you're talking about Port Royale 2, you can find some odd artifacts in chests in the water. If you bring all of them (I think there are 17 items in total) to your wife you'll get a novelty ship.

I can confirm that if you don't rescue your kidnapped wife, you get her back and the only cost is that she makes a little dig about you not being the man she married. The first time she was taken, I did the business and got her back, but the second time, I wasn't ready - 90,000 gold and ten mighty, fully-crewed ships are required, and at the time I had neither. I used to have five battleships but I mislaid them (how could I have done that?) so now I have ten galleons.

I had hoped that marrying a governor's daughter would make him better disposed toward me, but that didn't seem to work. The information wifey gives you is useless. Her only use is that, if you have the necessary stuff, the mission to get her back is fun, so I regard marriage in Port Royale as worthwhile. I didn't spend a penny on the marriage celebrations as I had earlier discovered that 100 units of meat, booze, and so forth didn't keep people happy.