aalenfae said:

Well, no.
In ANH, he serves as the storyteller, bringing us through the action of the film (and interpreting for R2-D2).

In ESB, he might be mostly comical, but he serves a key role in building the tension on Cloud City. Even if it's a small role, he serves the story in some way.

In RotJ, he's the ambassador to the Ewoks, who are integral in the Rebellion's success on Endor.

His presence on Endor makes no sense until they find the Ewoks, a species the Rebels were apparently entirely ignorant of until Han & Co. make first contact. His presence at Jabba's palace is not particularly logical either, as he does nothing useful during the Barge battle, and nothing of consequence leading up to that. Artoo w/ a few more holograms could have done the job just fine.

However.... in the prequels, C-3P0 does nothing for the story. Nothing at all. He makes a stupid naked joke in TPM, he bumbles around and has some stupid puns in AotC, and he makes some pointless remarks in RotS.

That is true, unfortunately. It'd be great if TC-14PO could do something useful, at least in TPM...but yeah, probably too difficult to pull off.