I think it depends to some extent if you plan for this to be a one-off piece, or something that looks like it would work as a level from a side scroller, for example. The latter would be easier, so to speak, since, to be honest, lots of side scrollers either ignore or marginalise vanishing points in order to stay consistent. You could stick with the current method of not showing the sides of buildings, but maybe futz with faking a downward-pointing camera (ie, show a bit of the ground, show the top of the tank, the tops of buildings, etc). It might work. Or you could go with something akin to the roof on Turbo's edit (show one side of the buildings, back of tank, etc). Alternately you could do a bit of both.
Given the current composition, Taking Turbo's edit further would probably involve the least amount of work, as the downward camera would involve redoing most of the ground and background elements.