>> If you buy the 13 ouncer, you pay less $ per ounce, but then you're left yearning for the 10 ouncer, and if you succumb - you wasted the money on the 13 ouncer. Maybe you're better off buying the best jacket which will last for years, and then eventually you can buy the best pack... No clear best answer...
That certainly is a concern. In my case, I generally just don't have enough fun money at any one time to validate those really high dollar goodies, and I can generally make myself happy with whatever it is I purchase. In those rare cases that I can buy something now and make an incremental upgrade later, I consider myself blessed. Since all of my retired gear gets passed on to someone else (son, scouts, etc.), it's never a waste.