"Esquire" to "Escuire" appears to be just a simple change of spelling.
The joke is that the shoeless bum with the raggedy top hat, clothes, and umbrella believes he can be just as classy, dapper, and suave as somebody in the upper class gentry simply by polishing his bare feet until they shine radiantly.
In addition to simple, silly gags and wordplay, Wacky Packages at this time would sometimes also poke fun at the different ways that product packaging would lure people in. The original "Esquire" packaging might have someone believe that they would be "magically transformed" from an ordinary person into an aristocrat simply by applying this polish to their shoes. Ah, a Cinderella, rags-to-riches story! Even today, ads pull the same stunt. Wear such and such makeup, ladies, and you'll melt years off your looks. The sad reality is that, having spent money, the elderly lady is still an elderly lady - just now wearing makeup, and the ordinary working Joe is still an ordinary working Joe - just with freshly polished shoes.
The "Rebell" Model Jet is another example of this expectation VS reality. I'd be willing to bet that of all the plastic models assembled by people over the years, less than 90% of them actually looked like the picture depicted on the box when they were finished. Hence, in keeping with "MAD" magazine humor, we get...
With both "Rebell" and "Escuire," a general statement is being made about what the product actually is VS what the company of the product would like us to believe.