A rare event when shinobi feast and crazy slot machine coincides would be the best. That would be a good time. Shinobi feast gives good rewards. you know it when you know that it's just 3 days compared to crazy slot machine which is ther throughout the month.

how often does that happen?

probably the best recharge event in my experience is the shinobi feast + weekly recharge (recharge every day at 50/250 ingot if i recall correctly.)

You need to recharge around 2k ingot for the medal, so you can spread it around by recharging 300 every day for 7 days. that gives you 3 spins on the itachi wheel every day. It's been a long time since we've had both in the same, like 2 months tho?

the other recharge wheels, the rewards are not great in my experience and I don't think i've ever seen them at the same time as shinobi feast. maybe just once.

another thing to look for is to have a recharge event and a spending event at the same time. Shinobi Feast + Shuriken (lucky balloons) event is typically good rewards, or a spending wheel.

Rare.

Just seen it once in 7 months.