While skins do NOTHING but look neat (most of the time) and have cool effects (most of the time) I do agree there should be an in client preview of the skin itself and not just a splash art since that's almost never a good representation of the in game model. We shouldn't have to go to a third party website to see what a skin or ward looks like on the Rift.
But until they add support for that here...
http://www.lolking.net/models
You CAN preview everything in game, including animations. Just not the sparkly effects.
But on the subject of trying Champs out, that's what Free Rotation is for. And before it's said, yes I know what you mean by trying them out, but this isn't SMITE where you directly control the actions of the God/Hero/Champion where its a REALLY good Idea to get a feel for how their kit works in a 3D Environment.