I agree that one person will make little difference, but that is all that is within my power. Just like an election, I only count as a single vote, but that doesn't mean that I should refrain from casting it. In this case, that would be a vote of no confidence.
In regards to buying stuff for other factions, one person buying will also go unnoticed. My purchases will have little effect on the final outcome. Besides, my interests are solely in 8th Edition Warhammer Proper; so unless they are releasing models that directly tie into that, I couldn't care less which factions receive love. To be honest, the current AoS model aesthetics are not in line with my particular tastes anyways; with a few notable exceptions (Warqueen, Lord of Change, Guant Summoner). I'm not saying that the models aren't well sculpted, but rather they are at odds with what I am personally looking for.
Now looking at the bigger picture, any money I spend will add to what is considered success by AoS, so I limit my spending on GW products.