I have three suggestions.
Firstly, the upgraded versions should also affect un-upgraded cards:
For instance, the upgraded death one should count skeletons and elite skeletons, not just elite.
The upgraded earth one should buff riders and gem-finders, not just gem-finders.
etc.
Secondly, you should add one for neutral element.
Thirdly, if there was some way to create these.
I though of 2 decent ways of doing this
1) You could a card in the style of Nymph's tears, that turns either pillars/pendulums or creatures (you decide) into a stone of the same element.
2) You could add a creature with the ability to do the above effect. (possibly the neutral one).
there is also a 3) you do both