I've never bothered to work out the costs and monetary worth. There's other qualitative benefits to getting out that some have mentioned - time with kids, new experiences, recharge out of the rat race). There's also hidden costs of staying at home you forget about. We are a family of 5 so one trip to the cinema in Sydney is not cheap, and a day trip to Taronga costs over $120. School holidays get expensive. So even a few weeks a year is worth it IMO, for more than just money.
We are planning to get out more since our recent acquisition. Aiming at least two weeks long trip once a year and a few weekends in between. Sydney>Fraser via New England highway last year, NE Tassie this year, Syd>Adelaide via the Darling River Run next year etc etc. Our kids love getting out even though iThingies are banned on camping weekends. They still talk regularly about our Uluru to Darwin trip 3 years ago.
We've also got a permanent van on the NSW South coast. We really need to use that once a month to justify the park fees. But we usually are down there for a weekend every couple of months and spend 1-2 weeks and Xmas and 1-2 weeks at Easter there. Those 4 weeks pay for itself if you look at hiring a house/cabin over the same period. Its an extravagance, but being 300m stroll to the beach on the edge of a National Park, but away from the school holiday crowds down in tent city is gold.
So with that and the CT, we'll have a lot of great family experiences over the coming years, but a really crappy looking garden