I actually use the green crystal: please don't nerf it for me or make it unusable in my deck!
I use the green crystal in a super fast bandit deck for rpve 10 using green affinity nomads, bandit lancers, and corsairs. Please don't make it heal per second for the green crystal, the instant heal of 400 could be buffed and still not be broken, so by all means do so, but for me changing it to a slow heal would be a nerf.
I use breeding ground to cheapen the corsairs, I don't get a fourth orb, instead I stick to 3 and spam green corsairs using offering on green bandit lancers to refresh charges beside a furnace of flesh + breeding ground. I also use shrine of war and incredible Mo. By using offering on bandit lancers I can refresh my spells as well which are all 3 orb. The deck actually works suprisingly well unupgraded. I used green nomads as well which can benefit from the crystal sometimes. And twilight warfare is key to the deck, helps the corsairs survive better since they do great damage, when you add lifesteal they are tough.
I do RPVE 10 super fast all the time with this setup.
The advantages of the deck are that you have 300 less power bound mid-game because you don't get a fourth monument -- I usually hit 12 XL squads before anyone else in-game; all of the corsairs get a damage buff because they all count as bandits to their ability, corsairs are cheap at 220, so you can build a large army fast and they move fast so you can keep spawning from a forward positioned breeding grounds. The green crystal helps to provide additional healing on top of twilight warfare and equilibrium -- it's nice because the healing is instant and can save a corsair from dying if an equilibrium is on cooldown -- I run 2 equilibriums.
Also, I actually like that the crystals impact affinities not colors, that's unique and cool, they just need some buffing I think.
My suggestion is to have them buff affinities still but give the crystals two modes each, and you can switch the mode the building is in as a structure ability, then have the two modes give different buffs that could work for different strategies. This would give more flexibility and perhaps even open up some new deck types. The first mode for the green crystal could be what it is now but buffed to 600 life instant or something. The second mode could be area effect, the crystal gives green affinity cards spawned near it a cost reduction, similar to breeding grounds, but on green affinity only.
Another idea is that the second mode on each crystal could effect structures while the first effects units, just some idea -- mainly I like the idea of two modes to each crystal (active and passive maybe) because that would be more likely to make it useful in some more instances.