Hey!

There are few ways of spending ingots correctly but in general you have to follow 1 simple rule (thats for recharging and spending): only recharge / spend ingots when proper events overlap. To give you few examples for both:

1) Recharging ingots is mostly best on a week that overlap Lucky slot Machine + 2 other recharging events, like Slots + Red envelope + Shinobi feast wheel or Slots + Red envelope + general recharge rebate or platinum (Ino event is also very good value but thats a bit risky so i didnt include it here)

2) Spending is more tricky and a bit depends what you really need. Probably most popular way of spending ingots is just converting them for double value in Naruto Froggy

Other option is waiting for another good week that overlaps 2 or 3 this time spending events in 1 single week. Mostly those are:

Fuku deals / Balloons / Time limited shop / General spending rebate