The best “value” in the cash shop other than the Deathknight armor (and considering that over a long, long period of time) is the daily gems, 225 gems (given over two weeks, and you can’t stack it) for $5, or 900 gems for $20 (and over the course of two months). All things considered, the conversion rate to something significant is still pretty poor, and it amounts to basically a nudge toward a larger goal or helping you stay ahead of the curve. With VIP chest access, this amounts to roughly 0.18 to 0.2 mythics (on average, depending on how many VIP you open at a time) per $20. Sunday’s daily packs probably have the next best “value” in terms of getting mythics, giving you roughly 0.1715 mythics (on average, counting the gem keys in the pack with their 1/1042 chance to drop a mythic) per $20, some of it divided into diamonds and the other the tiny tiny bump you get from gem keys, a good chunk of it being “guaranteed”, which is nice. The four celestials and 1000 souls are chaff, as you’ll likely get a couple celestials from 900 gems worth of VIP chests and 1000 souls from about 10 minutes of farming if you even need either at all.
Ring of Wonder’s bonus is additive. On top of an existing 100% gold bonus (you’d have at least this), you’ll be raised to a 150% bonus, or your resource earning rates will go from 200% to 250%, a functional 25% increase - less if you have VIP levels that give you gold bonus, and even less for souls (if you even need them), where you probably already had a 150% bonus from guild. Since gold has very poor individual personal value in even very large amounts, you probably won’t get a whole lot out of this unless you play a lot.
Some comparisons - for Ring of Wonder’s gold bonus to eclipse Daily Gems in raw “value” you’d need to be able to cover the ~600 difference in “gem value” before it runs out (counting here, relative purchasing power of a mythic if converting all resources gained into the thing that gives the best chance at pulling a mythic). This means earning 21.4 “gem value” daily for each of the 28 days that Ring of Wonder is active. Getting this from the 50% bump in gold bonus is actually very difficult, even with constant PvP farming.
If looking only at personal value, if you converted your extra gold gained into gold keys to try and get gems and glory, and use those to get future exclusive mythics on VIP chests and glory keys respectively, their highest possible values, you’d need to earn about 597 gold keys daily, which equates to 179,100 extra gold per day that you need to earn from Ring of Wonder being active. Opening these 597 gold keys will get you an average of ~9.45 gems and ~379 glory (after putting any gold gained from the keys back into more keys recursively), which equates to roughly the same mythic purchasing power as 21.4 raw gems on VIP chests. At an average of 600 extra gold per PvP battle (eg., a base payout average of 1200 gold, a generous estimate of an average payout that I get at endgame, as it would probably be lower), that would take about 298 PvP battles - per day. For a month straight. You would, of course, in the process of opening that many gold keys, get souls, low rarity traitstones, and low rarity troops which I assume you’ve already maxed and are therefore pointless. Similarly, if you are over level 1000 and hit the soul wall, increased xp and soul gains mean very little, especially at the functional increases you get from Ring of Wonder.
Pouring gold into legendary tasks are only better if others in your guild are also farming at an increased rate due to your increased contributions - which does happen, so you can’t completely discount it - but you can’t guarantee it will happen either. If your 20-25% increased contributions can get the rest of your guild to kick in even 5% more, you are already benefiting more than from gold keys. Of course, if everyone could match your increased contributions 1 to 1, then Ring of Wonder would far surpass the daily items in relative value, even just relating to getting items that can obtain future mythics - but this simply won’t happen in this reality. Otherwise, your guild as a whole gets a fractional increase in rewards and you personally get a negligible increase in rewards.
tl;dr - Ring of Wonder is giving you the illusion of value due to how this game’s economy works. A lower level player (that has already gotten a Deathknight pack) and has very high playtime and still working on their kingdoms or has difficulty reaching gold quotas might be able to get their money’s worth out of it, especially if they also need souls, but an endgamer that has all current mythics probably wont, unless their goal is just to give their guild a small bump.
Recommend either Daily Gems or Sunday’s dungeon Daily Deals.