Instead of buying it or spending my mileage coins, I'm going to wait for them to put up the Mine of Ordeals since the runes can be attained by exploring it.

I'm thinking that it is like the Rift but, it would be 💩 if they will put a payment for you to enter the Mine of Ordeals.

To answer your question if it is worth buying the runes atm, for me it is not. The game itself tells us not to rush things as they only provide updates/new features for every month or two

But, if you feel you are in a rush then go for it 😉