Unless you're filthy rich or have more money than sense, I would highly recommend not spending any gold on these events, regardless of where that gold came from.
If you must spend gold for imaginary items, you're way better off spending gold on limited edition units or crates because if you spend gold on these events, it's a statistical certainty that you will eventually waste a ton of money for absolutely nothing, and I mean everyone (yes that means you and you).
Like any gambling event, the odds are always in favor of the house. You may win in the short run, but if you keep doing it, you're going to lose.
I doubt the odds have changed much over the span of these events. They may have slighly fiddled with the percentages from game-to-game, but the "feeling" of variances that people report over any single event aren't really conducive to what the real percentages may be.
Bottom line, don't spend gold on events; it's a stupid bet.