remember that a long, long, long time ago (actually, 13 days ago) I was asking LL why there are double prim areas in mainland and if they pay the same tier as single prim areas?
well, they finally came up with an answer. The answer couldn't be more obvious, but they had to investigate thoroughly before giving one. Yes: Tier is the same.
Meaning: people that own land in double prim areas have double land capacity too, so they get twice as many prims as you do, and still pay the same.
And as to why is that? Because initial cost for land is higher and they can't terraform. Obviously they don't know how costly is a waterfront parcel in mainland and...
terraforming is ridiculous at best.
So knowing the "disadvantages", and aside for protected waterfront parcels, would you say it's worth something owning a parcel in single-prim inland mainland?
No wonder now why those huge spaces are usually empty.
If I were LL I would have created huge archipelagos instead of continental landmasses. And I guess it's too late for a change.
Definitely they get -10 when it comes to land management... 
Check your notecards! Figured I would get your attention 