As to gold: AFAICT, pikmin storage is what you should save your gold for. Vanity items if you like, too. But nectar is too easy too replace to make the storage upgrade worthwhile, and besides you shouldn't hoard it, but use it to level your pikminions. Petals are similar: ABP, always be petalin', especially since that's how gold is earned.
As to leveling: Once you have a squad size of at least twenty, it doesn't serm to matter much. Focus instead on churning through event challenges and levels will come on their own. IME, by the time you've walked the steps you have probably met the other requirements through regular play.