Those rules earlier are pretty good, but I would add another few...
Are we in a sale season? If yes, think twice. With so many different companies offering different things, and gamer gate being with a bunch of drunks for programmers, think two, three times. If you won't play it NOW, you will probably be better off waiting unless you feel that's it, you're done. Anything after that point, even free, will be a case of "oh well, this is where I was happy and don't regret supporting the devs at this price point."
And if the sale is on Amazon, be aware they price match. Be aware they can pull off better deals like nothing. Be aware of the 5 coupon and have games waiting and ready for them. It's likely everyone here has a notable backlog, just don't add to it yet, wait for the chance to use the 5 coupon, be happy.
All the sales right now should be thought of in the light of maybe it'll be in the January sale. This is why I held back on some already. This will cut into my coupons for that sale, so I may now end with leftovers, but that's okay. I made the choice and am happy with it.