1440p vs 1080p

The PB279Q is a 3840x2160 (4K) monitor, not 1440p.

"Worth it" is subjective. With the huge pixel count increase, it's "better" in that sense.

The VG248QE is 1080p 144Hz TN panel, 1ms GTG - so more of an e-Sports monitor, where high refresh rates and minimal input lag would be preferred over a "better" image.

Really depends on the hardware you intend to pair it with and the titles you wish to play.
 
Normally, yes, if Gsync or not is same, refresh rate is same too. 1440p panel has much more pixels than 1080p and thus more expensive. However, there are cheaper 1440p monitor that can be cheaper than 1080p. What CPU/GPU do you have? We can then decide if 1440p is suitable. For the two models you listed, pb279q is 4k, not 1440p and VG248qe is 144Hz.
 
It depends 100% on the combination of a) the system you currently have, b) the system you plan to have within the next 6-12 months, c) the games you're going to play, & d) what part of the performance you're looking for. The better your hardware (both now & near-term), the higher the monitor resolution/refresh rate you can go. However, if your favorite game is frame-capped (i.e. Dark Souls III capped at 60FPS), then getting a 144Hz monitor is going to be a wasted feature. By the same token, if you don't care about getting more than 70-80FPS, & are more concerned with visual quality, then a 144Hz monitor is going to be wasted on your gaming experience.