I think a dash of "tallest" has merit - here and there. It's usually good publicity for the builder, is very public city building (bordering on a feeling of communality at times) and sometimes city defining, and comes with a certain notion of 'progress' attached even if that is less lustrous than it used to be. The skyscraper, and the very tall skyscraper, have been an accepted urban norm for a century. Part of the giddy fun that is built into this architectural expression is it's inherent ability to gain great heights - and yawp about it. Whether that's a good thing or not largely depends on the quality of the building and it's context.
Height does matter, even symbolic height. This is the city that produced the CN Tower after all, which was seen as staggeringly high at the time, even if it did only surpass the Ostankino Tower by a smidge. That smidge did wonders for the city in terms of emphatically placing a big exclamation point declaring "HERE!" in all sorts of ways.
New structures probably won't have that kind of impact at about one thousand feet unless they're making it through different means - beauty, for example, vastly innovative technologies or green technology. The measuring line of a supertall is symbolic and a bit silly, but it is widely accepted. So, I don't think it's foolish to want to have a few, to show that we're up to it and keep things peppy
The supertall doesn't work in a vacuum, nor does anything else. As long as the quality is there and they work economically, contextually and aesthetically, (and not at the expense of other components of a liveable city) I wouldn't mind seeing a few myself.
________________
Actually, looking at the plans for the 1Yonge site, I think a few extra floors might help the tall building in the North-West corner, to help it stand out from the general pack.