So much of this discussion about overrated releases comes down to "I don't understand why people talk about this album so much," and usually the release in question is something that came out on a (relatively, for the ambient field) major label.
You wonder why people talk about Magnificent Void more than other Roach albums? I don't. It came out on Hearts of Space, right around the peak of that label's reach and influence, at the mid-90s peak of the relative mainstreaming of the ambient/electronica scene. You couldn't browse the ambient/new age section of a Tower Records without stumbling across that album and FSOL and Aphex Twin SAWII.
I'd argue those albums are discussed more, not because aficionados of those artists consider them the best albums, but because they were the highly visible, highly available albums at a peak time for the genre.
It's the same reason so many of these albums were ranked highly on the firstname.lastname@example.org
"all time best ambient" polls -- not only were they talked about a lot, but the CDs were owned by the largest number of people. Same goes for the FAX and Emit and Silent label releases. These were widely distributed in the early-mid 90s heyday of ambient, so everybody saw the discs in stores and everybody owned them.
In other words, I the frequent mention of these releases is more about the label they were released on, and the distribution those labels achieved during those years, than the albums really being highly rated in 2012 by serious listeners of ambient.
Having said that, I think SAW II is a masterpiece and Magnificent Void is my favorite Roach album!