I've been wondering something: What is Eddie's motivation in sucking up to Ward and June and other adults? What is he trying to accomplish?

The best I can figure is: He hopes that by acting excessively polite, it will provide a cover for his mischief, as no one will suspect him of doing anything bad. I'd be interested to hear what others think.

I think your theory is a good one.

He does tend to butter up his superiors because his father tells him don’t waste time with people who don’t count and why learn about a group of people you’ll never meet in business.

The best I can figure is: He hopes that by acting excessively polite, it will provide a cover for his mischief, as no one will suspect him of doing anything bad..

That was always my main suspicion. Sort of a pre-emptive guilty conscience.

I've read published accounts however, claiming his motive was to project himself in a peer capacity to the adults.

I guess that either is a possibility, But I think the latter is "over thinking" it. I believe that children are more likely to think in the former frame of mind.

and some people are just natural born car salesmen or worse - politicians (I had to throw that in !)

Eddie accused Beaver of long playing mouth but that was Eddie. He actually thought that adults bought his superficial banter. The Cleavers showed great restraint until Eddie went over the line like in the report card episode. Eddie wasn’t very smart for a smart A$$. I stole that from another poster.