i have contributed my fair share of such cards, but the impact is really changing the element in hand. off the top of my head-
the first one i made was convert a
to
creature, this would allow the darkness creatures to be implemented in a light deck, which i considered a weak spot of light at the time
the next that i recall was a water card that changed card costs of any element to water, this was fitting in water's synergy with everything theme
i also have permanents converted to earth and spells converted to aether, which i believe are also fitting on a thematic level
the basic philosophy for me is such changes would create a wide range of new applications, but at a cost of having to have an extra card and maybe some extra quanta in order to use the off-element cards. i still think its a good idea even though it hasnt proven to be very popular at any given point in time.