both, mickey and retsoor are right. a thing is worth only what someone else will pay for it, and only spend the money you can afford to lose. and yeah, pank is right as well, people expect bigger and better rewards without spending a thing.
with that said, i know it's very frustrating to spend anything, call it nuggets, bonds or in game money, just to get junk. but that's how it works and we all know beforehand that our chances to get junk are like 99.999999999 to 0.000000001 to get something really good. i compared it to a lottery, and that could go for as little as 50 cents per ticket, to 20 bucks, to $200 if you are buying a bunch of them. your chances per ticket remain the same. then take it one notch up, when you bet in horse races (something i don't do either, so don't expect me to understand the system) you can bet $1 or $1 million, depending on where you are placing your bet, for the same horse and the same odds. just because your bet is higher it doesn't change the odds, just gives you a better chance for a better reward or a better return. same way, if you have a million to spend in a casino or the tracks, and you are betting it to a clear favorite that will pay you 50% per dollar spent, then you know beforehand that you are about to lose 50% of your money even if you win; and if you are aiming for a surprising winner, you know you will hit a huge jackpot if you win, but your chances to win are minimal.
when you buy a premium chest you are not placing a bid for one unique prize. you are only narrowing your chances to get items of much lower value. you are paying so the junk you get from it is of better quality, instead of some fancy pants (that you would get in steel boxes) or something black (iron chests); and with that, your chances at hitting the jackpot improve as well. and yes, you are also paying for a chance at the jackpot, which you wouldn't get in wooden, iron clad, steel or precious chests.
i have crappy luck, that's why i wouldn't pay for what will likely be junk. that's, however, not the opinion of many others who not only buy chests with real money but also get great things in them.