If you felt packed into the Cat. 6, then the extra room will make a difference. With two kids, you don't really need the Murphy bed, but it does give you a little more room to spread out.
If you were fine in the 6, than the extra money may not be worth it.
We're of the "more space is better" mindset. You might want to consider adjoining cabins as well...adjoining Cat 7 may compare favorably to a Cat 4.