By your calculations it would take you about 3 months to make back the 1,200 you give up in smart rewards.

I'd say if that is the case it is worth doing as after that point you will be making more every month.

The only question I would have is: when you make a withdrawal from your Smartnode address does it affect the smartnode? If you need to restart the node then it might not be worth it having to wait the 20 or so days again.