Some serious infill and height is gracing SF. This area has changed so much in the last 10 years.
On the topic of observation decks, they are money magnets I feel. Even if it's 40% of Salesforce's height, given the lack of decks, a monopoly for the meantime with respect to decks will make it profitable. So long as the market and advertise it effectively.
Having a bar is a good idea. That alone will garner interest.