Gil wouldn't be a good idea as any Gil used for it would evaporate from the economy. Philo would be fine, or possibly even Myth (trade off buying a Myth piece for another chance at Coil 1-5). I think Myth would actually be better as if you let Coil just go on farm you risk everyone gearing every job in full ilvl 90, skipping content intended for them to complete (CT, DL set, AF+1, etc). There's a weekly lockout for a reason, but spending Myth to unlock another go at 1-5 I think would be a fair trade off.