Seems to me like most of these sales are just what the games should be in the first place. Why is Prison Architect $30 for a 2D RPG-Maker looking game that isn't even finished? And in the trailer when he said inspired by Dwarf Fortress....yeah, no thanks. That game is free and I still won't play it. And that's a game that's been in alpha for like 5-6 years or something now.
System Shock 2 $5, was $10? I get that it's kinda new to steam but I don't think they updated it or anything, and while it's considered a "classic" I honestly could never get in to it. Kinda like Deus Ex, never liked it - not even the new one.
A lot of these games I got far cheaper in a humble bundle, and only played like 20-30 minutes of, but at least that money goes to charity.
Kerbal Space Program is a good game I got at full price, wish I'd gotten the sale price. It's good but I just wish it were closer to being done. It's on like .202 i think...you can get into space and land on a planet (with some user made tutorials), but it's kinda like uhh now what.
The prices on a single game seem to keep changing at least on a daily basis, so I'm never sure when to buy if at all. It also kind of discourages me from ever buying a game from Steam at the normal price, because sales can happen randomly at any time. Like I bought KSP, then the next weekend there was a random sale on it with no announcement or anything.