@ShadowcatX, do you have a specific scenario in mind where Split Concentration would be troublesome?
Combat spells aren't sustaining, so there's no issue there. Detection spells use Force for their range, so there's a motivation not to cast them at Force 1. Increase Attributes is also dependent on Force, so that won't work at F1. Illusion spells would be candidates for Split Concentration, but I haven't found them to be game-breaking. Possibly the concern would be around Combat Sense or Increase Reflexes, but using reagents for those just makes them more expensive (albeit less addictive) versions of drugs.
Of course, much of this would come down to how much these new qualities would cost in terms of karma, but on the surface neither of them seem lamentably overpowered to me.