What kind of projects are these?

I'd say that $10-30k range is blogs with high search positions and established affiliate partnerships, but that's just my uneducated guess.

BTW: empireflippers.com seems to be down right now, possibly due to all the hype caused by HN audience.

Yes that’s correct. Usually strong search position with a few keywords. One I bought and later sold had an affiliate partnership already set up.

What's your main line of business, and what went into the decisions to buy those sites?

Did they all have revenue, and the owners just couldn't be bothered with the upkeep, and you figured you could? (Just going off OP's story here.)

They all had revenue and vetted by empire flippers (and myself).

I figured that I could either increase traffic or use simple strategies to increase revenue and then resell them at a higher price. I’m not sure what the owners motivation was for selling. Usually to buy something bigger is my guess.

Edit: forgot to answer one question. I had just quit being a minor partner in a VC and wanted to learn about online marketing, and also realized how much I valued freedom over my time over making more money. I tried buying, holding/improving and then selling websites for a couple years. I didn’t really love it - Google’s unpredictable behavior carries way too much weight.