The best recharging event for your range is platinum recharge.

Since they added it back you can recharge 300 ingots per day for 7 days and get the first and second tier rewards.

In the past the best used to be shinobi feast, but they removed the sure 100 coupons for the 1st try in the wheel so is no more worth it.

The best spending event for your range is group purchase.

You spend 99 ingots when 500+ people bought a pack and you get back 3 times the value (10 cave keys + 1 random drop + 1.8 seal scrolls).