I just had the same problem. Never really used the microphone for anything, but after trying to make a Facetime call, I realized that there was not much else than noise coming through. I tried the vacuum trick, and it did do something, so I think there must have been some dust in there as well, but it didn't fix the problem altogether, it was still very noisy.
What made the mic work flawlessly again was when I made some very loud noises into the mic, some handclaps very close to the mic input, to try overloading the input. After that, the noise floor dropped completely to a normal level, i.e. very low.
Being an audio engineer, it occurred to me that the software calibration of the input must have been screwed up as well, with an extra 100 dB of gain or something - and that is the sort of thing that can happen after a software update, so to me that's a pretty obvious explanation.
In other words, if the Dyson is no dice in itself, try overloading the input with some loud noises, while having the mic on of course, to force the automatic gain calibration down to a normal level. Come to think of it, this might be what the vacuuming actually accomplishes, if you keep the app running while working the [vacuum] pipe...:-D