Cardiff's policy of signing just a few quality players could either go very well, or very badly. On the one hand it introduces quality without abandoning their promotion squad, but I expect the new signings are on significantly higher wages, which could create QPR-like rifts in the squad. Also, should these signings get injured, you're left with just the championship side. I'm not sure whether they'd have been wiser to have bought 6 ~£5m players than 3 ~£10m, although I guess that kind of spending worked for Southampton 12 months ago. They appear to be building a strong spine to their side though, and they already had some players in their squad who should make the transition to Prem reasonably well.
Palace, the only signing that I'm interested by is Campana, he's the Spanish youth captain, but I fear he can't be that good or he'd be at a bigger club. Up front, Phillips surely can't be relied upon as a regular striker, Gayle is young and very inexperienced (and overpriced), and Murray is out until January. Thomas is probably Prem standard, but I don't think he's got the ability to carry some of the others. I think promotion came too early for them, so they're using the money to improve the stadium, training facilities, etc, so they're better placed for a promotion tilt in the following season.
Hull I think have made better signings than Palace, and I think have more players capable of making the step up. I think they've got the firepower, but perhaps lack in other areas.
Overall, Hull remind me of ourselves and Swansea when we got promoted, Cardiff are closer to Southampton, West Ham and QPR, whilst Palace are most like Reading. Whether they'll perform similarly to those teams or not remains to be seen, and will probably depend on a team or two collapsing, as well as their own efforts.