Bingowings said:
Threepio is Luke's property and like Han is attached to the Falcon, Luke is attached to Threepio.
Han could have kept the door shut on the droid but for a small bit of added effort he salvaged the droid from certain doom.
That's not the same as deliberately bringing him on a mission in a forest where his skills wouldn't seem to be useful (though they do turn out to be) and where his physical appearance and personality would be an impediment to success.
The stormtroopers were inside Hoth base at that time. By going back to pick up the useless robot, Han directly risked his life. Plus he had completely no use in ESB (yes he did tell the hyperdrive was broken but that didn't really help in any way). At least by brining him on Ednor he didn't directly risk his life and 3PO turned out to be crucial to rebel success on Ednor.
If this wasn't a fantasy film, 3PO would be painted and wearing camouflage. But this is Star Wars we are talking about. You have to turn a blind eye sometimes otherwise the primary thing that should bother you is the unrealistic homogeneous gravity field on all ships.
Bingowings said:
Alderaan has no weapons, they may buy them on the black market and funnel them to the Alliance but they would have to be hand me downs or in rare cases (like the Tydirium) stolen imperial equipment.
Anyone capable of making fighters would be nationalised by the Empire.
It wasn't just Alderaan who was supporting the rebels. Clearly they had many supporters, judging from imperial officer's conversations (Tagge, Jir).
And it is not like rebels bought out a star fighter factory on stock market lol. They secretly hired engineers and build their own factory hidden somewhere safe.