Vaderios:

His ghost in ROTS means that it has to be in ROTJ too.

Why? Luke didn't know Qui-Gon, so why should he appear to him? There's no reason to think anyone other than Jedi they knew appear to Jedi. And besides, Qui Gon isn't relevant to Luke in any way, so he'd have no reason to appear to him.

Timstuff:

The idea of the twins being born on Dagobah actually makes a lot of sense-- Lucas should feel stupid for not thinking of it, because it offered a perfect explanation for "there's something familiar about this place." If Leia can remember her mom, then Luke can remember Dagobah. ;)

It sure beats the cheese out of being born on some no-name asteroid cluster that just so happens to have medical facilities.

There's no reason the twins should be born anywhere special or relevant. The idea was to keep them safe and secret, so "some no-name asteroid cluster" is EXACTLY the sort of place they should be born. And it's called Polis Massa, anyway. And Luke's vague feeling of familiarity with Dagobah is more likely his sensing the concentration of the Force there, both good and dark side. And Leia's feelings about her real mother are very vague and don't really define any memory.