Are these decks going to be playable?
Devotion came out in the Theros block so any card with "Devotion to" will be in standard until about fall 2015 when the Theros block cards will no longer be playable in standard.

Some of the cards you will be getting for these decks will have been printed in the Return to Ravnica block (Pack rat, Nightveil Specter) and you will only be able to play these in standard till fall 2014 (whenever the set after M15 comes out).

Without knowing what cards will come out in the fall 2014 set, these decks may either still be around, dominate all the tournaments or just drop off the radar once the cards from Return to Ravnica block drop out of standard. Standard is always about investing into new cards every year.

The cards you do buy can be used for either Modern or for trading off for newer cards so investment is never fully lost, you just may never get what you paid (but my guess is the Gods will still have value after standard since they can also be used for commander)