We do the same (although it's a bit more than $50 - $65, maybe it's Sr vs. Jr?). If you look at the LS4 blades vs. the stock LS2 that is even in Bauer's higher end boot, there is so much more steel that it's worth the extra coin. Of course, that will only matter if your kid isn't growing out of his boot every 12 months.
But, you should be aware that not every blade is the same. The LS4 and LS2 have the same profile. The LS3 doesn't.