In my game I frequently see inactive sims arrive on a lot, stay there for a couple of sims minutes, and then just go away. Is there something I can do to force them to stay longer and actually use the lots?

The lots are fully decorated and active sims have no problem choosing what to do. The lot I notice it a lot on is the dance club. So maybe its the lot assigment being in Dragon Valley, rather than Bridgeport...? Also the local watering hole is highly unpopulair with my sims. Yet my park is hot stuffs.

This will not solve your problem, but I will just say that the attendance of a lot like a dance club, bar or hangout sometimes depends on its popularity. It is randomly determined every day and you can find out about it from the newspaper. Also, those sims who start working late at night have a habit of returning home. In addition, community places have preferred traits that make certain sims want to stay there (or not).

Have you tried Shimrod's Townies Out On The Town. Site required free registration though. But I've found the mods to be safe.