Well you couldn't have stated my own thoughts any clearer than that. I've always had a hard time looking at the minecraft youtube community when they just go through 30 miniute, short, poorly built maps that are just parkour or something when there's just perfect gems waiting to be discovered not just on Planetminecraft, but on Minecraft Maps and the Minecraft fourms as well.
And I don't speak for just city maps, and I don't mean to discourage small time builders doing their best: On the exact contrare, I've been doing my best to look through any interesting map I find, and then write a thorough and complete review to go over both the things that I liked, things that I think the mapmaker(s) did great, and things that I think the mapmaker could work on.
As for just city maps- I think the major conflict is that most people simply just don't have the patience to explore large, complex and deep city worlds like, for example, Broville. I myself have this map downloaded and I've gone to some lengths to explore the world in creative and see what secrets I can find. The thing is, it's so vast that I don't think I've even scratched the surface, and anyone with less patience would probably just walk down the street and be like 'meh' and log out, which is a huge shame. And unless youtubers found a way to spice it up, it'd probably be rather dull to the viewers as well, or encourage them to download it for themselves and explore.
And again, frankly I don't think this is just something to be considered with city maps- I also think it should be considered for adventure maps. I can rattle off an entire Top 5 best adventure maps that I've played from Minecraft, and I can garuntee you that for every one of them, there'd only be one or two videos on them and it's a 90% chance that it's from the creator themselves.
But in any case, I fully support your thoughts, and I hope we can all figure out a way to bring 3rd party city maps to the masses!
-Tra_kad
P.S. Your post is accepted- you type in English better than most native born English speakers that I know. x3
P.P.S. On the note of 'spicing things up for youtube'... I actually thought to myself that Broville in particular would be an amazing world for a Battlefield style Command-Point capture game thing. It'd probably take a lot of plugins or mods or something but... it'd certainly spice it up.