I think these cover-up/bury proposals would be great if we could wave a wand and make them occur, but they would be very, very expensive. The reasons to do such a project are:
1) to create more room for development or public spaces/parks
2) cover up expressway eyesores
3) improve connections between neighborhoods/bring together divided neighborhoods

While there is no way to cheaply repair horrible "urban planning" from 1945-1980, we should remember a few things about Detroit, referencing the three points above:

1) Detroit certainly does not lack for space for developments and parks, downtown or elsewhere
2) There are many ways to improve the look of our below grade expressways and their surroundings short of covering/burying them. We tend not to keep them very clean, well repaired, or surrounded by well landscaped grounds. That could all be done for far less money.
3) Existing streets and boulevards that cross 75/375 could be turned into beautiful boulevards with wider sidewalks, landscaped centers, etc.

I have no opposition in theory to the large transformational projects, when there is money sitting around to do them. That isn't in the cards, no matter who favors it, anytime soon. We should improve what we have.