Some of the bits are pretty pathetic in their smallness: bits of scenes clipped by censors (like all those pirates getting killed in "The Smugglers"), clips used in documentaries or other television programs for advertising purposes, 8mm offscreen footage. Random episodes have turned up on reels in Hong Kong and New Zealand.
I much prefer watching the entire episodes which survive, fairly easy to follow since summaries are available. Some of them are tantalizing. I would love to see "The Wheel in Space" in its entirety--that's the one that introduces Zoe, the Second Doctor's final companion, and my favorite of his--she's so much brainier than Polly (who screamed a lot) and Victoria (who was a bit less cowardly than Polly, but still screamed a lot); also, Zoe makes a great foil for Jamie, who is brave and loyal but not so much with the brain cells rubbing together. Zoe was generally very intelligent and logical and, though naive at first, learned from mistakes.
"Logic, my dear Zoe, merely enables one to be wrong with authority."
--The Doctor, in "The Wheel in Space"
I prefer Jamie to Ben, with whom he overlapped a bit. Ben's chief characteristic seemed to be his not-particularly-unintelligible Cockney accent; otherwise, from the little I've seen, he was pretty much from the same mold as the 1st Doctor's Muscle, first Ian and then the stalwart ex-astronaut Steven. Ben's physically a little smaller that those two, also. But Jamie had more of a unique personality which didn't really have anything to do with his trappings, the kilt and the fake Scottish accent (the actor is from Yorkshire). Jamie would rush into things, and make mistakes, and show if he was afraid or speak up if he thought something was a bad idea. At the same time, he had an awful lot of faith in the Doctor and, I think, a genuine love for him. And Jamie was protective, particularly of Victoria and, later, Zoe, though with Zoe he also seemed to feel perpetually outclassed. Their final departure, in "The War Games," is truly heartwrenching. It didn't surprise me that, in "The Five Doctors," it is Jamie and Zoe who are used to try and influence the Doctor's behavior.
Maybe I'll hunt up the novelization of "The Wheel in Space." The script can be found here.