Don' t get too worried if you missed something. If you hadn't noticed by now, they've already hit every sale you are going to see. They are just rotating through and we still have till the 22nd. If they actually do something off the wall I'd be surprised. You'll see all the daily deals again as a flash deal if nothing else.
As for deciding when to buy something, these days I just consider the likelihood I'll play it more than 5 minutes. Skyrim is a perfect example. While I love the idea, typically on all the Elder Scroll games I absolutely hate the combat. I put up with it in Daggerfall and Morrowind, but Oblivion just irritated me to no end and I barely played it at all. I know nothing has changed with Skyrim except it's prettier. I do want to try it just because of that, but it's a $10 buy at most for me. This is why buying anything under $5 is just fine, even if I don't get to it forever(or at all). It beats paying $40-50 for something I'll never play (Like I did countless times in the past).