Is Istanbul worth it? Hell yes. Incredible city with an almost unmatched history. One night though...there is no way you can do it justice. Just hit the highlights...Hagia Sofia, etc. Get a Turkish massage if you can...it's awesome.
Honestly, I would say none of your stays are really enough, even for tourist stuff. When you rush through things hitting the sights you don't really experience the city...it's just another checkbox...you're there physically but not really mentally.
You can't find sightseeing in Barcelona, one of the most architecturally beautiful cities in the entire world??
If I were you I'd cut one of those cities out, if possible, and focus on two...or hell even one.
Honestly, I would say none of your stays are really enough, even for tourist stuff. When you rush through things hitting the sights you don't really experience the city...it's just another checkbox...you're there physically but not really mentally.
You can't find sightseeing in Barcelona, one of the most architecturally beautiful cities in the entire world??
If I were you I'd cut one of those cities out, if possible, and focus on two...or hell even one.