Our opinions will, inevitably, be different. Our experiences will be different, and what works for me might not be applicable to you.
I have never had knee pain. Not once. I got into running for the first time in my life, this year, and my frist run left me sore in my calfs, but no knee pain. My third run of my life was 6 miles up and over a nice big hill near my college campus, and I walked out of that the next day like I've been doing it for years. I just have pretty resilient bones and joints; I think I have my mother to thank.
We went on a 3-4 mile hike for a school trip and I strapped 60 or 70 pounds to my back to carry up multiple tents, the ingredients for a massive pot of chili, and tons of water. I am still in my prime, and I want to milk it.
I will be the absolute first to agree with you on ounce-counting. I understand it, I am NOT one of those people that says "Lose 5lbs instead" when someone wants to know what toothbrush is the lightest. I do cut extra straps off my bags and I have a half-toothbrush. At the same time, I often think about "stupid-light" and when it comes to fabric materials, I can't cut ounces there. The lightweight philosophy lets me carry my credit card and phone in a ziplok bag instead of a dry-sack, but it doesn't let me rip through a raincoat. So I'm careful about what I choose.
So, for me, 15lbs is fine (although I'm closer to 11 anyways, I was just giving an example).
Now, as to the camera, I can find a D300s used for 700-800 if I'm patient enough. Secondly, let me put this in perspective; by spending $90, I got a Boreas 40L on sale. I could have possibly saved up $800 and gotten a custom backpack, but for my enjoyment-to-money-spent ratio, the Boreas does fine for now.
When it comes to a camera, if I pay a substantially lower amount, say, $100, I will not have access to the sensors, visual quality, level of detail, and creative tools of a full-frame DSLR. So, my enjoyment-to-money-spent ratio is very different. I love photography- I live it. So to spend almost a grand on a camera is not a big deal.
I will be selling my old camera as an offset- it's really only a $300 upgrade, or something like that.
Different strokes for different folks! My topic started broadly and then I focused my section of the thread with a little personal anecdote. Do not confuse this with me preaching the "right" way to do it. When I say "My 2¢" I mean it.