I don't have many bikes - but I now remove wheels and rotate them around various frames.
One nice set of wheels can be used on 3 or more bikes.

If you have nothing special - ditch most of the 27" steel wheels. Rotate a nice set.

If you want to really condense - rotate handle bars. A few handlebars could fit multiple bikes - just clip in the brake levers, use a piece of electric tape to mark height, and drop them in when you want to ride. Wheels and handlebars probably take about 5 minutes to line up - then you're off.

If you do both - you storage usage of space is probably cut down by 2/3rds.