Yes, the adjective/adverb contrast is a good point, tsuwm. I was aware of that but trying to steer clear of the question because it launches into a thread I was planning on the matter...but this might as well be it!
It seems, over the last 30 years or so, we have come to juxtapose our adjectives and adverbs with an increasing acceptability, and just dropping the -ly suffix of the true adverb form. Take the case of really/real, for instance, because it's the most vivid to most of us. Somewhere back in the '50's or '60's folks began to drop the -ly for emphasis..i.e. REAL hard. Then it found it's way into regular usage as in "real cool". In fact, part of my question being "when did this evolution to the loss of the -ly adverb take place?", I was surprised to find on looking into a '72 Websters that "real" is listed as a legitimate adverb. Now, I know that somewhere as a young schoolboy it was drummed into my head that an adverb always takes the -ly because I scold myself mentally to this day even when the other use is now permitted. There are a list of other adverbs that fit the really/real transition, but I don't have them offhand...will post when I find them, and invite others to do the same.
So, in light of all this, why should a word like mind-boggling be forced into such an awkward pronunciation by taking the -ly in the adverb, when words like "real" are now an acceptable adverb form? It doesn't make sense. But, then again, nobody ever said the English language always makes sense!
And, in regards to the broader question...can anyone trace the loss of the -ly further back than the '50's? If so, where and why? If you could help me solve this mystery that would be real cool, man!