So, you should always save up items like Seal Scrolls, Summon Scrolls, Charm Materials, Refine Runes, and Cave Keys or events. But, should you redeem the 100 you have or skip events sometimes to save up for a larger rebate. I will add new rebates to the list as they appear. I am only taking into account the same event items returned and where the optimum return on spending is at. So if you want some bonus item from large rebate, then take that into account for yourself.

Recruitment Feedback v5.0 (Seal Scrolls)

10 times - 1 scroll - 10% rebate

50 times - 6 scrolls - 12% rebate

100 times - 16 scrolls - 16% rebate

200 times - 36 scrolls - 18% rebate

300 times - 66 scrolls - 22% rebate <---Best Deal/Recommended

500 times - 66 scrolls - 13% rebate

800 times - 66 scrolls - 8% rebate

Minimum Scrolls to reach "Best Deal" is 264 using the refunds up to 200 to get you to 300 total. 500 and 800 only give ninja frags, so no extra rebates after 300.

Limited Time Recruitment VERSION 5.0 (Seal Scrolls)

10 times - 1 scroll (7 day) - 10%

50 times - 4 scrolls (7 day) - 8%

100 times - 11 scrolls (7 day) - 11%

200 times - 24 scrolls (7 day) - 12%

300 times - 44 scrolls (7 day) - 15% <- Best Deal

500 times - 44 scrolls (7 day) - 9%

Note, 7 day scroll do not count towards your total, so you need 300 normal scrolls to get to the best deal. This event is not recommended unless either you have more than 264 Seal Scrolls in your inventory, OR you are trying to use on a treasure that never gets included in Feedback event. This event is not limited by which treasure you pull from, only bond treasure doesn't count.

Summons Rebate (Summoning Scrolls) Version 6.0

10 times - 1 scroll (7 day) - 10% rebate

50 times - 6 scrolls (7 day) - 12% rebate

100 times - 16 scrolls (7 day) - 16% rebate

150 times - 31 scrolls (7 day) - 21% rebate

200 times - 51 36 scrolls (7 day) - 26% 18% rebate

500 times - 91 scrolls (7 day) - 18.2% rebate <-Best Deal, Recommended

You would think always go for the best deal, but this event almost always lasts 7 days, and every other week there is a monthly event to use 20 Summon Scrolls. So, your best bet is wait to do this event until the rebate and the monthly event are at the same time and then do at least 20 scrolls. Note: 7 Day scrolls don't count toward this event, so you need the total for each rebate.

Cave Exploration Rebate (Cave Keys)

50 Times - 10 Keys - 20% <- Best Deal

200 Times - 35 Keys - 17.5%

500 Times - 65 Keys - 13%

1000 Times - 100 Keys - 10% <- Recommended

2000 Times - 140 Keys - 7%

You can get the Jackpot prize at 1000 Times (well actually 1050, because you need one extra to do full luck spin). And the reward keys are limited-time and don't count towards event. So, I would always do at least 50 each event, and then save extra until you can do 1050. Which will likely only be once a year, unless you are really farming keys from events.

Refining Rebate 6.0 (Low/Medium/Advanced/Epic Refine Runes)

50 Times - 4 Advanced Rune - 8%

100 Times - 9 Advanced Runes - 9%

200 Times - 19 Advanced Runes - 9.5%

500 Times - 19 Advanced Runes, 8 Epic Runes (~12-16 Adv value) - ~6.2%-7.0%

800 Times - 19 Advanced Runes, 18 Epic Runes (~27-36 Adv value) - ~5.8%-6.9%

The difference in rewards is now even more varied. This is assuming 1 Epic rune is worth between 1.5 and 2 Advanced runes.. Just remember that if you are close to leveling and you are using Wish Credits from event to be that close, it will likely be worth spending 105 runes rather than stopping at 100. On the flip side, it might be better to wait until next event if you are close, but not using Wish Credits to be close. Then when the event comes next time, you can level for only a few runes and then use the wish credits to level up again.

Time-Limited Charm Rebate v6.0 (All 5 types of Charms)

25 Times - 5 Charms (1 box) - 25%

50 Times - 15 Charms - 30% <--Best Deal/Recommended

150 Times - 30 Charms - 20%

250 Times - 55 Charms - 22%

500 Times - 105 Charms - 21%

1000 Times - 205 Charms - 20.5%

Smaller Rewards after 50 charms used, so try to save up at least 50 charms for each event. I would not recommend saving for big prize unless you are getting lots of charms from events/coupons. Just go for which level (50/150/250/500) you can actually reach when event happens. And although it is called "Time-Limited", the rewards do not have a 7-day limit on them, it just means the event often only lasts 2-3 days.

Cultivation "Rebate" (Scrolls don't count)

level - cost - value - %

10 times - 90 - 133 - 148%

50 times - 450 - 558 - 124%

100 times - 900 - 1133 - 126%

200 times - 1800 - 2195 - 122%

500 times - 4500 - 5071 - 113%

800 times - 7200 - 7992 - 111%

1000 times - 9000 - 10072 - 112%

1500 times - 13500 - 14851 - 110%

2000 times - 18000 - 19674 - 109%

2 knocks against this event, rewards diminish as you spend more. And second, the scroll "rebates" don't count in event much like the 7-day scroll events. If you plan on spending some coupons on 5 nature chakra, wait for this event. Otherwise, best deal is to only spend 90 coupons (10 tries) on this event when it pops up.