Not as much as you'd think, in the daytime a 1080p 4mm can ID out to 15ft, a 4MP 4mm can ID out to 20ft, 5ft is not worth a reduction in low light performance of a factor of 10x when you can buy a 6mm 1080p Starlight and ID out to 22ft.. or just get a varifocal and get it right where your target area is.
Lets see, they made TV's in 320, 720, then 1080.. now 4k, which is ~8-12MP.. so your logic falls apart on that aspect if it were to remain true.
For outdoor security resolution is a minor factor easily dealt with by the proper optics, the major consideration is low light performance and thats where UltraHD cameras start falling apart, if everything else remains the same just packing more pixels into the same physical sensor space simply reduces sensitivity in low light conditions.. Megapixels dont mean dick, and more often than not the more megapixels the less photons it's capable of gathering.. for a 4MP camera to have the same sensitivity to light as a 2MP camera it'd need a sensor 2x the size, yet all 4MP cameras are 1/3" and all 2MP Starlights are 1/2.8" which if you know your factions means there actually smaller, not bigger.
Keep playing the Megapixel game and you'll loose, I've yet to see a 4MP camera from anyone that can hold a light to these 2MP Starlights.. cheap 4MP Cameras are largely a gimmick to separate ignorant people and their money.. If you want UHD there are 6MP, 8MP and 12MP big sensor and starvis sensor based cameras that outperform those lil sensor 4MP cameras day and night.. but when low light is most important they still get beat by the 2MP Starlights..
Dont forget more resolution and higher bitrates means more storage space is required to achieve the same thing; having a bunch of UHD cameras just yields you crappy low light performance while using up more storage space.. Zoom, learn to love it.. takes no additional storage.