Size does matter
I look at resolution vs size the other way around. That is, if you want a larger monitor, then you need higher resolution. Around 24" is where I would draw a line. I'm sure a 24" 1440p monitor looks better than a 1080p, but it's not as noticeable as say a 32" monitor. If you were to get a monitor under 24", I'd say to save your money and get a 144Hz 1080p.
I guess another issue would be how close you are to your monitor, if you're only a foot away, then you might want 1440p on a monitor under 24", but if you're 3 feet away, you wouldn't see any difference.