I bought an acer predator XB241H (1920x1080, 144hz) about a year ago, but I've since then upgraded my build. I've been reading a lot of people tell me that 1440p 144hz is worth the upgrade, but I'm wondering if the extra resolution is worth the money. My PC would be able to support those frames at that resolution, but should I just wait off? Or is it a good upgrade?
Not knowing your system specs makes it impossible for us to say if your system is capable.
1440p is all about pixel density. Most people are comfortable with the ~90ppi of a 24" 1080p display. However, once you get up to 27" and larger monitors, things start to get pixelated for the distance you're sitting from your screen. (this is a helpful guide).
IMO, 27" (in 16:9) is the best size for immersion at a typical fingertip viewing distance, and 1440p is best for that size from a pixel density standpoint (32" 1440p is the same density as 24" 1080p). Of course, more pixels to draw means you need more GPU horsepower to maintain the same frame rates as @ 1080p. That means more $$.
So, it's more about density than pixel count. TVs are a good example of this. Back when the average TV was 20-24", 480p was fine. As TVs have gotten larger, higher resolutions are desired.