I'm aware of that. However, that detail really is the only thing holding this leak up beyond the usual leak fare, much like the Wii Fit Trainer prediction was Gematsu's ace in the hole. There are a few (admittedly unlikely) explanations for the Tomadachi pic, like early Famitsu access. While that doesn't seem likely, when the entire leak currently hinges on that pic, I think it's a fair thing to consider. There have been numerous errors throughout the leaked pictures, so I'm waiting to see a little bit more definitive evidence before I believe anything. At the very least, I think the leakers are not to be trusted and I don't believe anything not directly in the pictures (no offense any leakers reading this, being skeptical is just my rule).
As for the Brinstar thing, that's really not all that surprising. Clearly, a huge amount of work was put into this leak if it's fake, so the inclusion of one picture of a stage which has been around for a decade is not all the conclusive. For all we know, the leaker had already put Brinstar in just by chance and didn't need to change anything last-minute. There are a LOT of old stages in this leak.
And I don't think adding more characters makes this any more believable. Sakurai has said they're not focusing on expanding the roster as much this time, but with 55+ characters this would be an enormous roster (a 16 character increase from Brawl, the biggest ever increase for a SSB game).