I nearly fell out of my chair at the "if you can't make it good, make it big..." line! Priceless, and too often too true!
However, I can't agree with a broad brushed condemnation of all things big. I mainly print 8x10 and rarely any bigger for a variety of reasons (mainly practical ones), but I know this much: a bad 8x10 will be a HORRIBLE 20x-anything. It takes a good photo to actually stand up to being "exposed" to such minute visual inspection.
And perhaps that is what Mr Michaels meant: you can't just blow up anything at all in hopes of making it more impactful through sheer size. I did not understand it as a condemnation fo all things larger than 8x10.
Also, even 30x30 prints do not "require a gallery" as is mentioned in the quote. That is another point that I think moves beyond size itself and into the realm of questioning wehter the artist actually has anything to say if he is making his audience so extremely narrow as to include only those who have access to a gallery. Its a matter of exclusion of potential viewers rather than a discussion of size as an artistic merit in and of itself.
Just my take on it - I am no artist,