I think you should leave this to the individual batter. For me personally I do not feel the need to have all buildings in HD, and so far HD bats have looked worse at zoom level 5, this is the zoom I use when making images for my MD.
As a more classical city builder, I always prefer to use an HD model whenever possible. For visual gameplay I spend most of my time at Z4 and Z5, but for screenshots and sharing my work, I try to focus on the street level: Z5 and hopefully Z6. The problem with this is that a single SD building can absolutely ruin a Z6 screenshot, whereas a single HD building will not do so with a Z5 screenshot.
Personally, if it were up to me as a BATer, I would offer everything in both SD and HD, and let the player decide where they want to go with it. There's already numerous buildings on the stex which are available in MaxisNight and DarkNight, why not offer the same option between SD and HD?
Hi tslater, welcome to the site and thanks for the input.
I am in agreement with Kwakelaar on this one, it will make more sense to let the individual batters decide. If people want to make SD, HD or both they can - and likewise people can install what they choose. Personally I am still keen to see how laborious it is to insert Z6 into a SD model - if that can work it sounds like the ideal solution.