So I've been saving all these Inscribed Secrets, Luxon Totems, Equipment reqs, etc

Is it a good idea to trade every quest reward thingy in for a key, for the event? Or are there better reasons to keep them or use them for something else......

The chests are ONLY affected in Nightfall.
Factions and Prophecies chests are untouched.

For the factions reward things, I'd suggest turning 5 in for a superior salvage or ID kit (Salvage 2k, ID 500 gold, your choice)

then I can keep my Factions things for trading in but I still have all those Inscribed Secrets, Kournan Coins, etc

Oh yea, turn those in for keys if you want (and can) .. so if they're nightfall rewards, turn them in for keys

In case you do not know, trade in 7 Trade Contracts for a ruby, sapphire, or diamond. The Rubies and Sapphires are worth ~7k *each*.