I think those are all excellent ideas. I also think there's more to the Pirates line not selling well towards the end of the first run than just poor set design, although that is an important factor for us, as AFOLs, it's less of an issue with a little kid who wants a "pirate ship".
If you look at Hollywood, in the '80's and early '90's, there was a lot of Pirate blockbusters. We had The Goonies in 1985, multiple retellings of Treasure Island across television film, The Princess Bride in 1987, a Peter Pan cartoon with Tim Curry (who you probably know as Dr. Frank N. Furter), Hook in 1991, but then Renny Harlin made Cutthroat Island in 1995 and it tanked. It cost $100m to make, it made $10m, the production company behind it went bankrupt, and it ended up holding the Guinness World Record for biggest box office flop ever.
1996 saw the release of Muppet Treasure Island, and there was nothing worth noting until 2003, when Gore Verbinski directed Pirates of the Caribbean: The Curse of the Black Pearl. It grossed $650m in the box office, sold $250m in DVD's the first year it was released, and Megabloks got the licensing rights for it. (I personally, saw PotC:tCofBP 3 times in the theatre :-p)
Then they kept on making PotC movies, and Star Wars for that matter, so Megabloks and Lego both sold a lot of toys. As soon as it looked like the Pirates craze was over for PotC, Lego released the brand new Pirates II.
Aside from having a very limited number of sets, they seemed to do pretty good. I searched high and low and wasn't even able to get Brickbeard's Bounty until about 3 months after the release.
As soon as Lego was in a position to sign a contract with Disney (which was probably influenced, in part, by the fact they already had the Star Wars license) they went for it.
In 2003, nobody knew PotC was going to be a blockbuster until a couple days into it's release. It took off, and I'm sure that if Lego had seen that happening they would've snatched up the licensing rights to it the first time around.
In conclusion: the rise and fall of Lego Pirates is directly proportional to how well Hollywood made pirate movies.
A couple side notes: I actually enjoyed Cutthroat Island, it has an awesome musical score, some pretty sweet swashbuckling, and some great action scenes. I loaned my DVD out awhile back and never got it back. I don't even remember who I loaned it to :-/