I have two five star snowman, teleport, fireworks, invisible and bat. I with that I can stay any of those things all the time. As soon as one is done its recharged for the next magic to start. Since it starts again right away its like making is longer only I have to click the snowman and teleport to use again right away.
I say if you ever think you want to trade it dont combine it. If you never plan to trade or think you will as a multi star then why not go ahead and combine. Its a lot of fun that way.
when my teleport was only two star it took a long time to recharge so I didnt feel it was as beneficial as two seperate would be. It wasnt until it became 5 star it became fun to have it together. With two seperates you can use the second one right away after the first so in a way better than two combined.