Very interesting topic Dillon, I love the question you present.
I actually disagree with people sometimes thinking Fire and Water don't "mix" together well. My question is why not? Why do these two elements not mesh well or rather, why do people think this? I have yet to see a legitimate reason as to why.
If you look at the periodic table the elements are simply matter in its most basic forms, they cannot be divided any further before getting just simple atoms. They differ between each other only their number of protons, that's it (not getting into ions and bonding here). Say you have iron and oxygen, two very different elements but they can be combined.
A very simply put example using the periodic table...
The spiritual elements can in a way, be looked at in the same manner. Under certain conditions Fire and Water work perfectly together. For instance the purification value of fire is used in a ritual to purify a container of liquid making it distilled water proper for usage.
A more literal combination is steam. In herbalism steam is useful for muscle relaxers and so on.
I can go on and on but my point is that using multiple elements, in complete regards to their properties, is perfectly acceptable and often does not violate balance.