I think the reason they didn't make any Luke/Leia jokes was becasue during Blue Harvest, Lucasfilm told them not to do any incest jokes.
Saw Something, Something, Something Dark Side today and it was average. It suffers from a lot of the same problems that have caused Family Guy to be a sad shadow of its former self. Namely, running jokes (that felt like they took even longer than usual, unfunny jokes and cutaways, and just plain bizarre decisions, like using the footage from Rocky IV (I did get a kick out of the Magnum bit). The Juicy Fruit, while a total blast from the past, was a complete waste of time. The beginning of the episode was for the most part awful and the second half is completely rushed. Mort as Lando is a complete and utter waste. The one funny joke at his expense, the reference to him wearing Han's clothes, was completely ripped off from Robot Chicken. Yes, I know Seth Green does that show but that still doesn't excuse the rip-off joke. All these neverending jokes just cover up the fact that the writers don't have enough talent to keep doing this show.
Still, there are a number of funny jokes. The opening crawl actually hits on all cylinders. The Dac bit was clever, as was Chris imitating Admiral Ackbar. Stewie's idea for "turning" Chris to the dark side was another funny joke. Peter's reaction to "I love you" was great, followed by the great gag as to what he looked like in carbonite. The last joke at the end, where the medical droid suggests that Luke should test out his mechanical hand on a hot dog had me rolling.
Still though, this was a clear miss for FG. Even though it's years past its prime, the show has often risen to the occassion for this special episodes. They didn't this time. I only hope the ROTJ spoof is funnier.