That seems fair to me because it results in a tax based on how much the property is worth to you specifically. The "value" may be inflated from real market value, but as long as that is true for everyone it doesn't matter.
Also if it's too much of a burden to value all these assets, you can list them publicly and let people bid. If you expect the government to protect your ownership rights, I think it's not too much to ask that you list your major assets.
Such a scheme could also require you to list a value of "all unlisted assets". If you try to hide a gold bar by lumping it in with all your trash, then the government can buy out and auction "all of razorunreal's unlisted assets" as a job jot. Companies would pop up specialising in identifying people with hidden assets to profit from them.
Also if it's too much of a burden to value all these assets, you can list them publicly and let people bid. If you expect the government to protect your ownership rights, I think it's not too much to ask that you list your major assets.