Hi there [enter your mark's name here] old friend...is what I refer to as 'sleazy'. A strong term I admit, but if you are going to send me an auto response, don't pretend like we're close buddies.
I would respect more something like 'You are the 159th signup we had today, send an email to [a real person] to request support.'
You are an extreme outlier and nobody looking to drive user engagement would ever write that email. But, then, nobody would use "old friend" in a welcome email and nobody reputable considers them "marks" so I am curious where to procure one of these windmills at which you are tilting.
These emails are targeted toward normal people, not social-discomfort-masquerading-as-efficiency people (because there are still a lot more of the former among developers than the latter) and normal people respond favorably to the appearance (which becomes the reality) of being valued and appreciated by people who they are looking to do business with.
That's why they work: because they connect at a real level. And it's not "manipulation" or any other carefully chosen fear-word any more than any other communication method is; it's simply--literally simply--how people are.
I would respect more something like 'You are the 159th signup we had today, send an email to [a real person] to request support.'
Perhaps I am just an outlier.