Hmm... I probably have a simplistic view of this, but not sure this is the case (the detrimental comment). Detrimentally in terms of overall development times? Sure. But detrimental in terms of long-term sustainability (appeal) of a vibrant, dynamic… and accessible Downtown for all? Not so sure…
Regardless of what the raw numbers are (meaning “empty/available” parking spaces in DTSJ on a given point in time during the day/night), perception often wins out over reality. If I’m a non-regular visitor driving around and the most visible “public” lots appear either full, or somehow inaccessible, then I’m probably going to be discouraged in coming Downtown (or in making return trips, etc.). Point being, the more available parking – as long as it’s strategically located – the better (I do realize that’s what your latter paragraph is effectively subscribing to)…
Anyway, even if we build-out the density Downtown for the next 50 years, IMO, we’ll still need the parking. The people living down there may not, as they have “built-in” access to multiple modes of mass transit, but visitors sure will. Fundamentally, I’d think that the better Downtown SJ gets, the more people will be drawn to visit it. As such, it’s worth pointing out that this Valley is already well-stocked (choked?) with hundreds of thousands of cars, millions of people… and a single light rail line, a single Bart line (eventually), a single CalTrain line and (maybe) a single HSR line. It’s nice that they all converge at Diridon, but, practically speaking, for anyone (not pointing the finger at you here, mind you) to think that everyone will just happily hop on mass transit to get to and move in and around DTSJ is sheer folly.
Back to your second point: a large garage that serves much of the Diridon area could work, but then you get into the “ugliness” of such a building, as well as the always vexing question of who will pay to build it. Is the City flush enough to do that these days (meaning without the deep-pocketed RDA it used to rely)? Seems doubtful (at least on the surface). Maybe if office buildings are built and tax receipts are flowing then the City can readily float bonds to pay for such an undertaking. I just don’t know if the City is ready for something costly like that.