Irregular verbs exist for a reason... they're the verbs that get used the most, and the irregularities are how people either eliminate redundancy or add additional shades of meaning that most normal verbs can live without.
Ditto, for "silent letters" in English. They're how we disambiguate homonyms (ex: to/too/two).
If English had official "tones" like Mandarin, we could distinguish between meanings of "fuck" used as a verb in writing, to visually indicate things like sarcasm. Actually, in a way, English *does* have an informal "system" of indicating the equivalent of _tones_ -- quotation marks, underlines, italics, boldface, and wikitext markup.
Any conlang that *really* gets used by **real** people as their "real" language will quickly mutate and become as irregular as English or Spanish.
Japanese only has two irregular verbs that are used often, and another eight or so that are used rarely, and it's an _old_ language spoken by a lot of people. Likewise, Finnish and Chinese both have under five irregular verbs, and Turkish (I'm told) has zero. There are lots of other ways to increase information density per unit of written information to reduce ambiguity. I think that's important for an actual used language, but it doesn't have to be accomplished via irregular verbs. Word location and order, for instance, does a great job of displaying subject/object relationships.
I agree with your point that things like sarcasm, satire, humor, will be expressed by bending language rules, in any actual used language. I just don't think irregular verbs are a necessary emergent property of used languages.