Sure, $300 sneakers are ridiculous, just a little above the scale of $235 hoodies (I hit that mark with a Belstaff hoodie - nice, and very cool futuristic design, but still ridiculous) and $500 jeans (though not as ridiculous as $800 jeans.) All this things are luxuries, and particularly frivolous ones at that, although not as extravagant as 100K watches (what the hell is that all about!)
I think that as long as you are generally responsible with your money, you should be allowed your frivolities. But seriously, let's not say that the "quality" makes a luxury a non-frivolous expense. You can wear a $20 Lee hoodie (actually, my The Cast hoodies, costing about $130 apiece, are actually just printed on Lee 50/50 hoodies) and $30 jeans, and they will be just as serviciable as a Spruce or Loopwheeler hoodie and a pair of Jomons, or 5EPs, or Dior x Eternal 811s, or whatever takes your fancy.
As for the Y-3's in question - I've seen them, and they are definitely a step above usual Adidas quality, but not worth between three to five times the price of regular Adidas. Nor am I particularly impressed by the design or colorways, although they are nice. I would pick them up for $100, maybe, but would definitely not pay full freight.