In today's market I would wager a big fat no to property values going down. And as you mention, these are people with multi-million dollar properties so, world's smallest violin.I like this one! Contrary to what the other poster said about it being just a "same old square building", sometimes simple geometry is best. I'd rather this next to me than something that tries to do some "break up the massing" and "stepping back" stuff and then have it end up just looking messy. The materiality on this also looks like it could be decent — hopefully!
On the subject of the neighbour's house value going down, well, it is not the obligation of the City to preserve peoples house values and stop development on main streets in order to do so, but is that even something that happens? Does property value even go down when something like this is built next to a house? I question whether it would happen even in normal times, but the market is so astoundingly out of control right now that I can't imagine someone's house price in this location especially would actually decrease. And with such a central and valuable location I imagine the people living next to this will see their property value continue to rise for quite some time. And if they don't like living in the centre of a major city where there will be midrise buildings very reasonably built, they can sell and recoup those millions. Not a bad problem to have. Wish I had a valuable conveniently located house I could sell for millions!