Thing is, those prestige classes are mostly a gimmick in IWD. In BG2, they made sense as you could only customize your main character whereas in IWD, you customize the whole party. Not sure if the class kits are exactly the same but if they are, keep the following in mind.
The avenger druid gets max STR and CON reduced by two but they get 3 mage spells? You'll be customizing a spell slinger who will get those three spells anyway so what's the point in this crappy class?
The skald sacrifices some bard abilities for better fighting capability. In other words, a class that does 2 jobs badly, what's the point of this class?
The assassin can envenom their weapons........too bad IWD is filled with undead and constructs that are immune to poison. Consider the amount of enemies you face in IWD, backstabbing then getting surrounded is a really dumb idea.
The paladin kit that gets a bonus against demons? How many demons are in the game? If you don't dawdle, there are a grand total of 5 demons. 5!!!! The end boss, the two cornugons that accompany him and two glabrezu in TOTLM (more if you dawdle and let the summoners spawn more of them). Great kit............NOT!!!!
The wizard slayer is another garbage kit as there aren't many spell casters in the game anyways. At least there's more than 5 though.
The beastmaster will be in a real sorry state as they can't use any metal weapons. Problem is, the staff Conlan sells is the best staff in the game and you don't get any good clubs until HOW (unless EE adds new clubs and staves).
There are more but if these kits were tweaked for IWD, I'll take back what I said. If they just cut and pasted them in IWD, then most ain't gonna be useful. When you can customize the entire party, you should be making a party based on their strengths and making them compliment each other and a lot of these kits remove certain class strengths and replaced them with gimmicks.
Still, the sorceror, archer, barb and berserker are good for IWD but they ain't worth the cost of the EE edition.