The wording of Wild Arcana (errata notwithstanding) states
As a swift action, you can expend one use of mythic power to cast any
one arcane spell without expending a prepared spell or spell slot. The
spell must be on one of your arcane class spell lists and must be of a
level that you can cast with that arcane spellcasting class.You don't need to have the spell prepared, nor does it need to be on
your list of spells known. When casting a spell in this way, you treat
your caster level as 2 levels higher for the purpose of any effect
dependent on level. You can apply any metamagic feats you know to this
spell, but its total adjusted level can't be greater than that of the
highest-level arcane spell you can cast from that spellcasting class.
Does this mean that since the spell doesn't "need to be on your list of spells known", you could in theory cast any mythic version of a spell at the cost of two mythic points (one for wild arcana and one for the mythic version)?
Best Answer
Short Answer:
Unless you have a very generous GM, no.
Longer Answer:
Casting a Mythic Spell:
(emphasis mine)
Since you don't know the mythic version of a spell, that clause doesn't apply. Since that is the only path to Mythic versions of spells, it doesn't look good for using Wild Arcana to cast Mythic versions of spells.
So, how, exactly, do you cast spells with, Wild Arcana?
Since the Mythic subsystem doesn't add the Mythic version of spells to any class spell lists, Wild Arcana wouldn't let you cast a Mythic spell that way, either.
And, finally, both the Mythic Spellcasting ability and Mythic Spell Lore feat exist, which both strongly suggest that the only way to cast the Mythic version of spells is to take the feat and/or ability.