My answer is about the same asthe4nitz.
Verandas are expensive given that you are most likely not going to use it very much (when ever I've priced it in the past, is seems that it was about $100 per day extra???).
However, having a private veranda is great. When you wake up in the morning, you can get out of bed and step outside and watch the sun rise without taking the time you get "ready" for the day the way most people would before going up on deck. It's also great to just step outside and enjoy the veranda, just watch the sea roll by just before you head to bed.
So basically, I've you've got the cash, do it. If you're tight on cash and you're more interested in doing things on-board and at ports than just relaxing on your veranda, then it's better to put your money towards doing the other things you like.