The sweet point for me has been iOS 6-7 support. There's little that iOS 7 has that I need to use, so a few conditionals here or there haven't been a huge deal (tintColor has been the only significant one). This contrasts immensely with trying to support back to iOS 5 where so many new things were added after (e.g., autolayout) that you end up with huge chunks of redundant code that differ only in the approach taken to get the end result.
My apps' interfaces are entirely customized, so everything looks roughly the same across the major versions. I've shifted to a flatter appearance since iOS 7, but I've held onto certain things from older ones that I like better such as borders on buttons where the button status is not clear from the context, filled toolbar icons (I hate the stenciled ones), and a shadowing level somewhere between iOS 6 and 7.
My apps' interfaces are entirely customized, so everything looks roughly the same across the major versions. I've shifted to a flatter appearance since iOS 7, but I've held onto certain things from older ones that I like better such as borders on buttons where the button status is not clear from the context, filled toolbar icons (I hate the stenciled ones), and a shadowing level somewhere between iOS 6 and 7.