So it's explosive vegetation for 1 mana less, but the lands will be colourless until you can give them another turn to turn on?

I guess I don't feel right about it being an enchantment. I guess if this was in a set with a lot of land tokens then it's ability is relevant outside of the two it makes but still. I think this is a good idea but Firstly; ability to turn them into coloured sources should be a part of the first ability Secondly; I feel this should be a part of a larger card. Like if it was and you created tokens. Or maybe if it was a creature instead of a enchantment. Then you can tap the creature to use the second ability.

I presume desert tokens would be a larger mechanic in the set, so the static ability turning all your lands into Evolving Wilds is the main part that makes it worth being an enchantment

It is as Dude said. Desert tokens would be the Clues/Treasure/Food of a set, so the abilities on this card are intentionally split.

Or evolving wilds-like could be its own token type. Consider-

Create a Terrain token. (It's a colorless land with ", sacrifice this land: Search your library for a basic land that arrives tapped. Shuffle.")

That could be an interesting idea, though it would exist in a different sort of set, I think.