Haha, wasted?! If you're planning to go until end game, I consider inventory expansion as probably one of the most practical and valuable things you can buy with jewels, at least for weapons and accessories (which I also have the cap maxed at 400 & still run out of space for accs daily). Eidos of course don't matter as much, unless you're like some space whale. Even then I'm not even sure if there are enough available to warrant the limit raise there. Maybe to store even more xp fodders, but nah not worth it for me at least.
And yes, I am indeed saying that people are able to keep up with each event's weapon playing something like 3 hours a day for the course of that event without playing 16+ hrs a day like me. Like I've already repeated 3 times, there are literally people in my very union who do this. Not sure why this is hard to believe. Are the general populace really that inefficient when it comes to farming?