Is it worth it to upgrade to 240hz?

Yeah diminishing returns for sure, I find after about a ~x3 increase or ~72-90FPS any smoothness gains start to drop off fast. Your current monitor can already hit a x4 - x5 fps increase in most cases so your covered.

Films also have naturally occurring motion blur from the camera shutter speed which can vary from film to film, which gives additional smoothness not found in games(unless added in). Saving Private Ryan for example used 1/198 rather than the standard 1/48 shutter speed.

So a extra + x1 FPS increase(x3 -> x4 - x5) may help the smoothness in that case due to the loss of motion blur but ultimately not really needed. Games also benefit from reduced input delay, which is not relevant for video playback. So for games the extra is far more noticeable.

In saying that I do have a 240hz monitor which I've tried with SVP @240FPS. The main thing I noticed if anything in regards to video playback was that camera panning/motion was more clear(not really that much smoother) at 240hz/fps.

When it comes to motion clarity it mostly comes down to how long a pixel is continuously visible for and that the response times are fast enough to keep up with the refresh rate on sample-and-hold displays.

Running at 240-FPS did use a bit more system resources but I found it wasn't an issue at all for me, so I just left it at 240-FPS.

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Diminishing Returns

Framerate -> Frame time/New frame every;

24-FPS -> 41.67ms
144-FPS - > 6.94ms
240-FPS -> 4.17ms

24-FPS(41.67ms) to 144-FPS(6.94ms) gives a 34.73ms(500.43%) improvement

144-FPS(6.94ms) to 240-FPS(4.17ms) gives a 2.77ms(66.42%) improvement

So based on the math alone the jump from 24 to 144-FPS should give a ~x10 times larger improvement in perceived smoothness than the jump from from 144 -> 240-FPS will give you.

Yeah, is a few things to consider with BFI/Impulse but it can make motion extremely clear.
Some examples; (video @24fps)

x3 (13.89ms of persistence)
No change in brightness/contrast
Reduced motion artifacts (interpolated frames) vs x6

x3 + BFI =144hz (6.94ms of persistence)
Clearer motion @6.94ms
Reduces brightness/contrast
Reduced motion artifacts (interpolated frames) vs x6

x3 + BFI + Strobe Pulse Width@10 =144hz (1ms of persistence)
Very clear motion @1ms
Reduces brightness/contrast
Reduced motion artifacts (interpolated frames) vs x6

x3 + Strobe Pulse Width@10 =72hz (1ms of persistence)
Very clear motion + extra headroom for pixel response times**
Reduces brightness/contrast
Reduced motion artifacts (interpolated frames) vs x6

**Combine with VT increase for even better motion clarity
https://forums.blurbusters.com/viewtopic.php?t=8946
Note that this can only be done on select monitors which are capable of doing this.
IE Able single strobe at 72hz and have a scaler which can handle large blanking intervals(VBI).

Also of note its likely you will only see an improvement in videos which are using the full vertical height of the screen. Meaning it won't help as much when a letterbox is used.

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x6 = 144hz (6.94ms of persistence)
Clearer motion @6.94ms
No change in brightness/contrast
Technically smoother motion vs x3 (72fps)
Increased motion artifacts vs x3 (72fps) (interpolated frames)

x6 + Strobe Pulse Width@10 =144hz (1ms of persistence)
Very Clear motion @1ms
loss of brightness/contrast
Technically smoother motion vs x3 (72fps)
Increased motion artifacts vs x3 (72fps) (interpolated frames)

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The loss of brightness may not even be an issue if you have headroom to increase the monitors brightness to offset the reduction of brightness caused by BFI and/or Strobing.

240hz is not bad choice for video playback as it divides evenly with all the commonly used frame rates including after adding in interpolated frames in most cases. Just not 72fps.

240hz
Suitable for 24, 30, 48, 60, 120, 240 target framerate

120hz
Suitable for 24, 30, 60, 120 target framerate

144hz
Suitable for 24, 48, 72 target framerate

60hz
Suitable for 30, 60 target framerate

Personally I don't use 72fps at 240hz as it doesn't fit evenly. Needs frame blending, pulldown or VRR etc to be used. x3 is generally considered most optimal overall but not if it also requires the use of frame blending, pulldown etc. Which is more of an issue for 60hz monitors.

I would aim for either 48, 60, 120 or 240 after interpolation unless you have VRR working with video playback.

I think 120fps(or 240fps) would be the best all round target to avoid both pulldown and still maintain peak perceived smoothness on a 240hz monitor.