Expanded Towns and Cities does a good job with expanding the towns and cities in Skyrim. It doesn't change anything inside the main cities with their own cells like Whiterun, Solitude, Windhelm, Markath and Riften so you can use JK Skyrim, Dawn of Skyrim, etc. It does have quite a few patches available as well which may help. It comes in an All-in-one version and a modular version if you want to pick and choose which towns and cities to overhaul. The mod doesn't really improve textures i don't think, though it may add some new ones for certain buildings. It's been a while since i used it. http://www.nexusmods.com/skyrim/mods/13608/?
