I always seem to fill up my city and have constant complains about needing more workers or jobs or whatever but it doesn't seem to increase in density until after a really long time. I am wondering if there is some trick to get the density to jump up quickly. My approval is often above 75% but it still takes forever to get higher density.
Lower taxes to like 7%. They get constant tax break happiness boosts which really increases the speed they upgrade to higher densities. Parks also help, $ money parks will make them happier without increasing land value I believe, good for when you want a lot of low wealth workers.