One of the neat things about plasma donation is that you can do it way more frequently. If your arms can handle it, you can donate as often as once a week.
Personally, I have a recurring appointment for every two weeks during my lunch break. I spend an hour hooked up to the machine, drinking a coffee and reading a book - it's pretty chill. There's emerging research indicating that there may be health benefits to donating as well - you are basically doing an oil change for your body.
I sure wouldn't say 'all'. The first years of your mortgage you are paying the bank more in interest than you are knocking off the principal.
A $300k home with 20% down and an interest rate of 3.5% on a 25 year amortization schedule will see the buyer paying $8k in interest versus $6k towards the principal at the start. Over the course of the mortgage, the $300k home will cost $420k thanks to the $120k in interest the bank takes.