Slaved said:
I do not see people taking something like Flaming unless someone in the party can cast Greater Magic Weapon. I do not see people taking Ghost Touch unless there is a RolePlaying reason or the game is heavy on Incorporeal foes.
I do see people take flaming damage even without characters to cast greater magic weapon.
Even for those with power attack and a two-handed weapon, a +1 enh. bonus is effectively +3 damage, whereas elemental damage is more. For those that aren't two-handed power attacks, the advantage is much more clear. And, consider that greater magic weapon is an effect much easier to come by than all kinds of special abilities.
Many of the weapon enhancements are fully worth their price, and reducing that price by means of removing the scaling factor and thereby built in limitations is asking for trouble.
And, like I said, it's still just more fun to use the crystals as written than to allow combining them! The whole point is to allow cheaper access to exotic abilities which you'd otherwise never take. Why don't you take these abilities otherwise? Because it's such a huge trade off. You don't use that Lawful weapon since it's just +1 and despite the DR, your weapon focussed specialized mastery+otherwise optimized weapon just bashes right through the DR more effectively! So, you provide crystals which have
few trade-offs. You can now attach that ghost touch effect without serious troubles. Would you ever attach it if your "primary crystal" was already loaded with 10 other effects? It's
easy to find 10 other effects at a low level and low cost, so that's not a far-fetched issue!
The weapon crystals work
well as is, and would be overpowered if stackable, and furthermore, would be less fun in-game. If you
really feel the need to make this, then balance it (but I still don't recommend it): that means, make it much much more expensive than merely 50% more, and make powerful crystal require powerful enh. bonuses (for example, if you stack a +1 requiring effect with a +3 requiring effect, require that the resultant crystal is +4 or better). Again, I think that's a
bad idea, but if you're insistent on stacking these effects, it's only reasonable.