I'm pretty sure elemental bonuses do not exist. For example, you cannot say Aether has a "skill denial" bonus when it is the only element with skill denial effects (there no costs, that would not have the bonus, to compare to). Similarly, other bonuses you listed may not have basis is that there is nothing to compare to.
I'd like to give I do not think Air has a "creature control [cost reduction]" bonus. On the other hand, any cards which would be cheaper than "normal" (these cares are Fog Shield, Thunderstorm, Shockwave vs. Dusk Mantle, Rain of Fire, Lightning) are simply "knock-offs" that are cheaper simply because their effect is less powerful. The only thing this idea has going for it is that Unstable Gas may have free creature control added on, but I believe that is more thematic than formulaic.
The only identifiable "free elemental bonuses" are HP for Earth and Creature Cost Reduction for Life, and not all creatures in these elements are affected by these "elemental bonuses", so they are not truly elemental in the slightest.
I would like to propose an alternative way at looking at it: element-specific mechanics. These include lobotomize ("skill denial", as you called it) for Aether, drawing cards for Time, randomness for Entropy, outrageously high HP for Gravity. The difference is that these mechanics are neither unique nor universal, but would be strange out-of-element (or would at least have a higher cost, not necessarily in quanta).