Downtown SF and SJC were quite ugly during downturns before tech came to the rescue. Market street until recently was still suffering from blight brought on 40 years ago.
If I got that correct, then I would first say that there are massive numbers of people who want to live in SF who have been kept out by the $4000 prices, and lowering it to $3500 or $3000 would bring in far more people.
Further, thinking only in terms of service workers and tech workers misses a lot of what goes on in the city, there's a ton of people in between.
But even if I'm wrong, then having a huge number of vacant apartments is really good news for all renters in the city. It puts pressure on all other landlords to power prices. It changes the market segmentation, and drives improvements in prices or apartment quality for all market segments adjacent to whatever price the conversions initially target. There is no downside to a bunch of vacant office space converting to vacant apartments.
One problem with mass conversions, and in general the way that SF has done planning—zero change allowed for decades then dumping a bunch of new stuff in a small area—is that it takes a long time for the new neighborhood to gain all the character of a neighborhood, for example the little shops, the community groups, etc.
