Well, if the Dreamstone was created to protect it from Lavos, then that would explain that Terra Tower would have no Dreamstone, being from the Reptite Dimension, where Lavos did not land. However, with this theory there is still the problem of why the Dreamstone was there before Lavos landed. And since it was once used as currency, it would have to have been there even before Ayla's time, since she was the only one who had it then.
There's another possibility with the Dreamstone/currency problem that no one has mentioned--that the Dreamstone became currency after 65,000,000 BC. there's a span of time unaccounted for in which we know little about, next to what we can determine about the rise of Zeal and humans using magic (Sunstone, then Mammon Machine). It's entirely possible that there was limited dreamstone before Lavos's arrival, but that then after Lavos arrived, the planet made more Dreamstone to set up the possible destruction of Lavos. In this sense, the Dreamstone may be volcanic in origin, since the center of the planet is where the planet's power would likely be most concentrated. So the planet could infuse the molten rock there with planet energy and then erupt it out through the many volcanos of the Prehistoric Era.
