I'm only jumping in here because I do know the scriptwriter (Carter) fairly well, and have spent a bit of time asking him about some of the things you're talking about. There are several problems with leaving the script as translated, one main one being that the jump from japanese to english just isn't funny. Meowth, in translated japanese is about as stodgy as you can get. Jessie sort of makes the cut across the language barrier, although it's not with humor - it's really her attitude that makes it. Brock's not funny when he goes girl crazy either, and a real scene killer would be to let Max say what he says when he's dragging Brock out of the room. They *all* can be funny, but they're not in translation.The Big Al said:The script writer would likely just translate the script if left to themselves. Also don't forget LoT was dubbed a different crew altogether. The dub script is actually very close the original in the main series. It's the paint edits and music edits that were annoying. And putting a western joke in place of Japanese joke that wouldn't work in English is fine by me (as long as they aren't corny).
There are a lot of characters just echoing what was previously said, which must be more interesting or expected in japanese ("I'm going with Charizard!" Reply - "Charizard, huh?" Not exactly whiz-bang dialog).
Finally, it appears that the japanese are much more forgiving of the lip flap (which doesn't match at all in japanese) then the american market - I would say the english looks at least 100% better - like it really was written for english.