Hello there ripvsbis, i know many players and know everything about power. First of all - your "Power" isnt really showing how strong you are. Even with 480k power you can kill players with 800k power. Currently i am 47 lvl player and my power is 1 million. Most players of 40-50 lvl have 250-500k power - this is pretty small ammount, this is barely enaught to handle story quest monsters, not mentioning cerber kills attempts / PvP or Elite Bosses. There is no real reason to rush by levels far forward, by taking all available experience bonuses - the best strategy is to not use Labyrinth, Caribbean Pirates, Guild Benefits and attack monsters only if you need loot for item craft, untill you become stronger.

To be succesfull player at 50 lvl, you need:
a) Cianna, Calvin, and Saffron heroes with atleast 2-3 stars and Shayd / Alexa / Rhyze as last hero.
b) Heroes should be equiped with atleast 20 lvl items (pink) in 5-items sets. For having 5 items from set - you will get defence and HP bonuses, for 6 items you will also get damage and morale bonus.
c) Your equipment should be upgraded atleast to 15 lvl.
d) Each hero should have runes: Bane, Vitality and one of the following: Dodge / Block / Physical defence / Critical / Magical Resistance (all yellow awcors). You should have them atleast at lvl 5. Its good idea to equip yellow Morale Rune+6 for Cianna, to instanlty skill-stunn your enemy during first game turn. She also Stuns Baal / Cerber / Elite Bosses / Quest Bosses.

Now about Gems:

1) As Freyaa said - use them to exchange for 1,800k - 1,900k coins at Fair. Also there is blue stars 2-5 gems each, as well as 5 gems for star insinde Labyrinth (Discount event tile). Use coins at Rune Temple.
2) Use gems to open additional socket inside items (1 gem for item 20 lvl, 10 gems for item 40 lvl...).
3) Use gems to reduce item upgrade time, if you going to sleep for example and still have like 90 minutes cooldown till upgrade queue will be ready - you can cut it with 1 gem to put a fresh one research for the long night cooldown (like 10+ hours). Note, game will consider 1-119 minutes as "2 full hours" and will take 1 gem for each 2 hours of cooldown.

About 54 lvl player - i think at this lvl you should have over 1 million power, because of many rune slots. Players at 60 lvl are just crazy, they have over 2 millions power, so you will become easy prey for them, they will attack you very often to steal from you non-stop.

Also, beware of some game tricks:
- do not attempt to unsocket 4 lvl magical-gem out of item - it will cost many gems (like 100 or so). Bigger magical-gems will demand more.
- do not buy Saint cards, the rewards are random, you can get useless magic attack for Warriors and critical hit for Mages.
- first realm change will be for free, second will cost you 150 gems, tho it dosnt warn you about 150 gems, so care. Realm change is good to reset arena rank, to be able, to farm gems from weak opponents.

I hope it helped, sorry for too big info text, but i wanted to be usefull