Hi there! Welcome to Fantasica.
The premium tickets are roughly the same as the 4-hour CD free prize contract on SBT. They're considered a stepping stone as you get better stuff. The best way to use them, though, is to save them for either creating units to feed your Amber (check the forums a bit better about the procedure), or to convert them to Leana points in Leana's shop.
As for the 4M DL packs, the odds of getting a 6* is 50%, and they even give a tradable potion to use either in events or as currency. To be honest, there are better ways to invest your money than those packs, but do as you see fit. Just remember - there is also a good chance to get a 5* on those packs - around 40% or so.
Though i'd hold everything if i were you. We'll eventually get the Game Mash rewards in a day or two, so do your decisions once you've won said prizes.