OK, now I see where you're coming from. I think you're better off using Elements of Magic or Mythic Earth for combining powers.
You can mimic other source materials with the True20 magic system, but it's strength lies in having powers that are versatile. Fire Shaping is a good example here, as it replaces many fire-themed D&D spells with a single power, and an innovative player can come up with new uses if the DM is comfortable with setting a Difficulty (the similarities to skill showing again).
However, combining effects from several powers is not straightforward and in some cases it may be better to come up with a new power or feat to enable the new usage.
Elements of Magic, however, seems to match your mental model precisely; because of that it flows much faster and with fewer rolls when creating new spell effects on the fly (and you can work out the DC ahead of time for your favorite effects).