Bingowings said:
"In ROTJ the plan to rescue Han from Jabba's palace, if it exists at all doesn't make sense"
To address some of the supposed weaknesses of the rescue plot (In a side note, compared to some our recent geek mega blockbusters TDKR, Star Trek, and any Marvel film that feature truely insane scripts, the plotting in ROTJ is like a meticulously reasoned logic puzzle) I offer the following:
The team plan is... Lando goes in to scope out the joint (He may have been there for weeks, who knows, it isn't important). He gives Leia and Luke the low down and they hit on the clever idea of Leia going in disguised as a bounty hunter with Chewie as irresistable bait for Jabba. She'll free han, Lando in his guard disguise will free Chewie and with the droids in tow they'll all make a quiet exit in the dead of night. They all agree but Luke plans to wait as backup incase anything in this deadly situation and VERY risky plan goes wrong.
Which indeed it does!
Luke guesses that he might be searched for arms on his way in to the palace before getting anywhere near Jabba so he has already hidden his Saber inside R2 (Assuming wrongly, that he'll be able to get it if talking to Jabba doesn't work). Unfortunately R2 has been assigned to the sail barge so Luke realises he needs to improvise and tries to grab a blaster before falling into the Rancor pit. Then when they are taken to the Sarlacc pit R2 and Luke improvise again, R2 sees his chance to get Luke the saber. Luke gives him the nod. He gives Lando the nod that he's gonna try a rescue. Lando nods back... the gang all pull together and the rest is history.
Or putting it simply (To quote Bingowings comment about the merits of ANH), they...
"Somehow wriggle themselves out of the situation with a mixture of plausible luck and decision making that makes sense"
I rest my case your honor.