I think it is like blowing your breath into a bowl of water. The surface of the water bends and ripples, but if the water is deep enough, you cannot penetrate to the bottom of the bowl. A person in Gaseous Form is unable to exert significant force against objects nor can he damage them. Because a person in Gaseous Form lacks density, it follows that buoyancy will force him to the top of a liquid. Unless the liquid in incredibly viscous this would be accomplished pretty quickly and it would take a very deep liquid or a very high viscosity to prevent this movement before the end of the spell. Honey is not viscous enough to stop this effect.
Wind Walk is also capable of creating a magical wind that whisks gaseous characters along at about 60mph! Good Luck figuring that out. Because it relies on air as a transport medium, I would rule that it cannot penetrate liquids.
Creatures that swim in the water are effectively engaged in a form of "flying" when you think about it. They move their fins to displace liquid and propel themselves. There are crucial differences. Creatures that swim aren't normally capable of flying through the air. Creatures adapted to flying through the air are seriously impaired when trying to swim through the water. The Navier-Stokes equations are central to our current understanding of fluid dynamics (which applies to movement through the air as well as movement through a liquid). These equations also explain how creatures are adapted to moving through either air or water and why they then become ineffective at moving through water or air respectively.
The Fly spell, however, does not use wings or fins to provide propulsion or buoyancy. In other words, it is does not rely on the properties of the fluid the character is immersed in. Instead the character is propelled by.. what? a generic force of some sort. Hence Flying (as the spell), should work just fine in any liquid. Movement penalties would still apply, of course (for example, if movement costs double when walking through a liquid, then it ought to cost double to Fly through the liquid). Also, the rules for upward and downward movement might not apply (depending on the character's buoyancy). If a character would normally sink, then the rules for upward and downward movement apply. If he would normally float, then they might work in reverse or not apply at all.