Since both games have sequels, would it be better to buy the original games first, so that I'm not downgrading when I buy the second? They've all got great scores anyway so I figure I should own them all.
Hmmm... Tough call. I'd say you can skip the first loco roco. The second one was much better and not really tied together. However, with Patapon, I'd get the first one for sure. The whole story of Patapon is awesome, and the first one teaches you how to play better than the second one. So Loco Roco, eh.... You could get the first. Patapon- get the first for sure. And if you're wanting a fun, quality, cheap shooter, check out Syphon Filter: Logans Shadow. Great game.
They both have demos on PSN, I'd say play them first. I didn't enjoy them enough to buy the games. Edit: Should mention this is the US store, not sure about other stores. Either way there are plenty of sites online where you can download demos from outside your store.