The game doesn't know how to handle too many sims, so you're likely not going to find a world populated with so many that you "meet someone new every night". And places are deserted at night because that's how the game is set up, sims go to bed at night and there's no lots that are set to be populated in particular at night. A custom world won't change that.
So if I put down a ton of really tiny houses and say populated them with AM or just dumped the max limit of sims inside each one would my game explode into a bfbvfs?
You can, however, mod the game so that places are populated at night. If you want your town population of all ages to freaking love hanging out at the park at night, I'm pretty sure there are values you can change to get that to happen.
There is a mod made by Shimrod101 that sort of does this here:
http://ts3.tscexchange.com/index.php?topic=3954.0I will look at that mod and see how he did it. I can probably convert it into making sims come out at night and during the day. Shimrod101 mentioned some of the values he changed. It will just take a little tweaking.