Visuals are great and having ‘correct’ and fine looking visuals is awesome. Yet a game is way more than just looking at pretty things. Just like you say, it is the experience that matters and that can be achived drawing simple lines with stupid looking stick figures if need be.
Trying to make all visuals perfect will kill your motivation. Maybe it’s just me but I find it very stressful.
Your example is great. Allow me to put some dents in it.
Creating a dozen ‘filler’ NPCs serves no purpose. You feel prepared but actually you are not because you had spent your valuable time on pointless things like irrelevant NPCs instead of maybe focusing on the contant or creating something interesting/important/memorable right in the bar.
You see what happened there, right? You overprepared and it got totally ignored but at the same time you underprepared because you didn’t spend your time on things that truly matter (like the contact in the bar). That is what Alex and I are saying.
To make it a bit more concrete, next time you can concentrate on a single event and on a single motivation for the contact and maybe one other important NPC that is also present in the bar. Or maybe some important NPC (a villain perhaps) has an agent in the bar whatnot.
As you can see, I only focused on what is important for the story and nothing else. Everything else can be shot from the hip during the game but this way it has a simple structure and the story progresses forward no matter what the pesky players will do.
Also if you like having lots of NPCs and whatnot ready, I suggest that you use random generators for that purpose. If one of your players wants to talk to a dude, click on a button on a website to create a full NPC with character traits and motivations. I’d like to call this Preparation on Demand ™ lol.