Allocating money towards goodwill IS the smartest strategy possible. As Carl mentioned, it allows for amortization at 15 years, which is faster than real property land (no depreciation) and the depreciation for buildings. Thus, the Buyer pays less in taxes.
Perhaps more importantly, the lower the value on real property the less likely it is you are going to get a property tax increase. (If you are buying a park for $1MM that the county appraiser has on the tax rolls at $200K, which is common, get ready for the pain, unless you use this strategy.) The allocation has to be reasonable but the reality is that a large portion of the value in a MHP IS the permit (the operating business, i.e. goodwill) and NOT in the land or physical improvements. Really? Yes, would you pay $1MM+ for 10 acres of dirt on the outskirts of town? No way, as the adjacent ground is worth 10% of that. But, would you pay $1MM if it had an operating business with an NOI of $100K (grandfathered in and with permitting rules that create a barrier to entry for competition)? Yes, you would. And there you have it, you are buying intangible value - you can amortize intangible assets for income tax purposes AND you cannot be taxed on them by county appraisers (in I believe any state).
Final bonus for the seller - if the county/state have sales/transfer taxes or stamps then the seller will have to only pay these on the allocated portions of land/improvements.
Anybody who tells you not do an allocation with goodwill is ignorant or a fool.