To answer your question if you should keep buying platinum, yes you should if you can afford it and like to indulge yourself on this game. But do it for fun, because nowhere is it stated that opening a certain number of locked crates guarantees an item you want. It is based solely on luck. Spend your platinum knowing this fact. Platinum can be spent on a variety of things, opening crates is only one of them. Elixirs, ankhs, mythic pets in egg form, respect kits, plat exclusive vanity, you can buy it all and sell smartly (at the right time) to save up gold.