What sort of parties do you have? A car weighs about as much as 25 people? Call it 10-15 people plus furniture, sofas ? What's do you want to put on top? Tiles need a reasonably solid base hence the conc.

The basic principle is that the whole floor needs to be inflexible and non compress able i.e. Rigid otherwise you will get some compression under the main tracks where you walk, the substrate will compact a minis clue amount every time you walk over it even with paviours this can happen, look around your area at the driveways.

A mud flor is great but not flat and lower in the middle than the edges.you can always add more but will you want to be re levelling your floor?