There's a difference between a group that offers to lease land with the promise to improve it, vs. a group that already has leased land, has already improved it, and now wants to renew the lease. When you talk about getting the use of public land without paying, shouldn't the cost of improvements that will be used by the public (as the facilities in Balboa Park are) be counted as payment?
Yes, the improvements are a form of payment. The local BS council has promised to make $1.7 million in improvements to their camp, in addition to the $1 in rent and $2500 in administrative fees that they pay the city annually. However this lease was not opened for competitive bidding. It is possible that another group might have offered to make even greater improvements. Also, the public can question whether those are the improvements they would want. The park bureaucrats have apparently been trying to get rid of all the private groups on the park for a while. Only 14% of the park is freely open to the public because of all the leaseholds.
The Boy Scout facilities are not exactly available for public use. As a park-goer you may not stroll through the grounds. It is available to other groups only on those occasions when it is not being used by the Boy Scouts. Those groups have to pay a fee.
To use the Disney analogy again - they have made substantial improvements to the land under their theme parks, and they make it open to the public for a fee. Should the cost of their improvements count as a lease payment?
I don't know how the original lease was written, but the ownership of improvements is undoubtedly covered. On National Forest lands, for example, the leaseholder generally retains ownership. The downside of that is that when the lease expires the owner must remove all trace of the improvements. In other cases the improvements become the property of the landowner. I wish the District Court's filing was available online - I'm sure these issues would have come up.