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The environment will affect any monitor, so don't blame the MBP for that.
A new monitor has significant benefits (and downsides) but you may not need one as badly as you might think.
The vertical viewing angle (affected by the tilt of the screen) is my biggest problem with the MBP screen for colour accuracy and brightness. I wear eyeglasses and the monitor can seem like I am looking directly at it (i.e. the screen is perpendicular to my line of sight to the centre of the screen) and yet it usually is not. A small-ish change to the angle can make a big difference to the intensity of bright reds, for example, and to the details that are visible in those reds (as on flowers). A whole lot of edits can be avoided by getting the monitor angle right.
Nowadays I routinely put a small rectangular card end-on against the screen with one of its corners near the centre of the screen, and then I make sure that the edge poking towards me from that corner is aimed at my eyes. Thus it becomes very easy to confirm that the screen is perpendicular to my line of sight and then the colours and brightness are far more consistent. That in turn will make prints more consistent.
Horizontal variations in viewing angle are relatively insignificant compared with the vertical angles.
The retina screen on my iPad seems to be better in this regard and so I can see a retina MBP in my future once they give it more external interface ports.