“Would of” is simply incorrect grammar. It has nothing to do with dialect or pronunciation, nothing to do with the evolution of language; it is just grammatically incorrect. Phrases such as “I would have attended but I was busy” are “conditional perfect” constructions. They use “would have” together with the past participle of the relevant verb (in my example, “attended” being the past participle of the verb “to attend”). I learnt Latin at school and you cannot learn Latin without learning about grammar.
My current pet hate is the incorrect pronunciation of “the” when it precedes a word beginning with a vowel. It should be “thee” end not “ther” end, “thee” EU not “ther” EU. Happens all the time, newscasters and weather presenters – who should know better – being among the principle culprits. It is sloppy and sounds dreadful. You don’t use the indefinite article and say “a end” you say “an end” for a very good reason. That’s why there’s a difference in the pronunciation of the definite article.