I came up with a few more tips. They're more like an update than full tips, hence the 1.5 in the title.
Step 3.5: If you have a Lego store in your area, get to know your Lego professional. A good relationship with these people can go a long way. I've gotten loose parts and sticker sheets from people who work at my local Lego store. One Assistant Manager even asked what I'd like to see on the PaB Wall!
Step 6.5: Make sure to use sales, and use them for your greatest benefit. If there's a Buy One Get One (BOGO) X -- where X is some sort of discount -- sale, make sure you buy two sets of the same price to maximize the discount.
Step 7.5: Sometimes it ain't worth it. If you're buying a bunch of sets at full price to get that little $5 polybag, you're paying too much.