Any question answered...

Is there any point stumping the extra cash for Ultegra chains/cassettes/Chainrings over 105?

Probably not. Unless you want a full matching groupset.

Also, if I'm buying this kit and the pulley wheels look a wee bit fucked, should I replace those too, or are they just some bit of kit I ride til they fall off?

You might as well, they're fairly cheap.