Infrastructure generally doesn't scale linearly. So while one person doesn't have much of an impact, at some point you're going to have to invest a lot of money scaling.
I just don't see even 100k rich non-services-intensive people as being likely to cause a problem. What SF should do is get rid of the previous stupid payroll tax and Ron Conway/Ed Lee's even worse gross receipts tax and institute an income tax of n% on residents or those working in SF. Maybe make it progressive (just set it as x% of someone's California state tax bill?, maybe +10% so it'd be about 1% of gross income?).
Then, having 100k people making ~$300k/yr (reflecting capital gains plus wage income) and consuming <$100/yr in city services in some towers along the eastern side of the city would be awesome.
$300mm/yr in extra tax income would do a lot.