Re. inserts ... wouldn't it have to write an entire page of null bytes, so still the same data size?

Logically it shouldn't need to do anything at all with a new page - the snapshot won't care because the page didn't exist at the time it was created. Following that train of thought makes me wonder why there is any overhead at all unless there is some requirement on the index pages or any of the system-type pages - maybe contention on whichever set of pages determines if the snapshot file holds the page to look at? Am I missing something obvious here?

re. read performance ... I wouldn't expect a great deal as there shouldn't be any locking (snapshots don't lock because they are read-only, correct?). I only asked because the article covered all the other obvious scenarios - there are probably a number of good questions that could be answered on the read side - does the snapshot have its own procedure cache entries etc.