I'm curious as to your reasoning here. You'll need about 21,000 gold keys to mythic the next kingdom's new common. Any keys spent now that don't get whatever common you are hunting as of now to mythic before the new kingdom drops are basically wasted, because as of now, you only need about 20k gold keys (opened between silverglade release and now) to mythic that common. Just a few weeks later, you'll need 21,000 gold keys total to get that one to mythic. And if you already have silverglade's common at mythic (it hasn't been four weeks since the last common yet, right?), you just get a small amount of glory and a pittance of gems.
I normally use my resources as follows:
Gold Keys - only spend on new kingdom releases. Everything they can buy is long since mythic and I have hundreds more of every color of minor than I need to trait every troop in the game currently and am outpacing the release scehdule on minor stones.
Gems - VIP chests on Mythic releases only
Glory - Ultra-Rares and above in troop packs to mythics, commons and rare ascended a couple times unless I really need the Arcanes (not many left on that front). Otherwise, save as emergency stash of event keys
Event Keys - New legendaries in old kingdoms - get one and move on. New kingdoms - get legendary to mythic.
Gem Keys - Dump them if I don't get the exclusive mythic in the first 50 VIP keys.
Seals - Dump them when my guild hits 40k seals for the small chance they'll contain something useful other than guardians (spoiler: usually not)
Glory Keys - Dump them after new kingdom release for the small chance they'll contain something useful after thousnads of keys.
The entire cycle leaves me possibly moving up on gems on a given month, but since there was one mythic I ended up spending 9k gems, 600+ gem keys and 1000+ glory keys on and not getting it, all of that can disappear in a flash. I basically have no chance at ever obtaining any prior released mythic I have missed because of this. If I altered how I opened keys to maximize chance of prior mythics instead, I'd end up with less unique mythics overall after a period of time, which is not something I'd want to do.