I agree with BCooter. Use the system that best facilitates your process--workflow and subject matter. I've used just about every film and digital format. Cameras are simply tools.
Wood shop analogies: 1) C-clamps serve one purpose and bar-clamps serve another. 2) Making dovetail joints with hand tools is different than using a router and a jig.
For landscapes, stick with your 30+. As far as versatility goes, it's hard to beat a d800 and complimentary lenses. I like the trilogy--14-24/f2.8, 24-70/f2.8, 70-200/f2.8.
I own the first two, but opted for the 70-200/f4 VR.
MF has its advantages, especially regarding the ability to record nuance in color and tonality. FF 35mm is great for portability, speedy AF, high ISO, and in the case of the d800, resolution.
Your P30+ files are plenty robust. It's a fine landscape MFDB. Resist the temptation to buy something new when something not so new works fine. I often use woodworking tools that are over fifty years old.