As someone who has a bit knowledge of physics and math, I can already tell you that
we cant calc "energy shifts of the entire planet" and even then, the results would propably far to high to be accepted.
Wan didnt create the tree of time, it was already there. All he did was seal Vaatu and trap him inside the tree. You can read it here:
"Legends state that the Tree of Time's roots bind the two worlds together and is a source of great spiritual energy. In the era of Raava, the ancients used to commune in the hollow of the tree to connect with the great cosmic energy of the universe, before Vaatu was imprisoned in the tree by Avatar Wan. A book in Wan Shi Tong's Library recalls the legend of Vaatu's imprisonment in the Tree of Time. Elders believe that Vaatu is trapped by a strong spiritual barrier from which he cannot break free, provided that the two spirit portals are sealed by the arrival of Harmonic Convergence. If the portals were opened during this time, the amplified spiritual energy caused by overlap of the two portals will be enough for Vaatu to use in breaking the bonds that restrain him, leaving the mortal realm vulnerable to becoming enveloped in darkness" - from the avatar wiki.
"Harmonic Convergence is a supernatural phenomenon that occurs once every ten thousand years. When the planets align, spiritual energy is greatly amplified, causing the spirit portals at the North and South Poles to merge, while an aura of spirit energy envelops the Earth. During this event, Raava and Vaatu must engage in a battle that determines the fate of the world until the next Harmonic Convergence. However, after Raava merged with Wan, becoming the Avatar Spirit, it became the Avatar's duty to battle Vaatu in the Spirit World near the two portals that connect the two poles of the physical world." - avatar wiki
"Due to the amplification of spiritual energy during Harmonic Convergence,
the entire planet is covered by spirit lights, starting from the poles." - thats a feat we could eventually calc, but it wasnt done by Raava or Vaatu.
"Yes and the feat would be absorbing that energy to form the Avatar Spirit and using it whenever going into the Avatar State." - About that:
Wan used the energy only once to merge with Raava and thats it. He doenst use it every time he goes into the avatar state for several reasons: