Volty, you are absolutely right the value of the lease would be governed by what you can do with the facility concerned and personally, I have no insight into the scope of the lease in question. If it also does cover the outlying (& ever expanding) mud mountains then absolutely current and future values will be effected in consideration of any cost required to make those areas of use for other activities.
My presumption is that the current promotion would sell all of its business interest i.e. the company, inclusive of Speedway license, lease and all other assets. Is that worth 1m? Well, it is if someone wishes to pay it and of course the current owner wants to sell and frankly I think the answer to the latter is a no, and I can understand why that is the case given that after 3 years DH must feel he is making progress with the project and wants to see it continue as a successful business under his stewardship.