I think that with all AV electronics, it is difficult to tell quality differences from looking at the manufacturer specifications. There are many products that look similar on paper but perform very differently.
There is lots they don't tell you as it is generally in their interest to make people believe that mass market consumer versions are close in quality to the uber expensive launch versions. The first 2 Sony 4k projectors, for example. The $25k launch model (the ES 1000) and the newer cheaper version (the ES 500) at over $15,000 less. The advertised specs would lead you to believe that the only real difference was an insignificant 300 lumen drop in brightness. Not a bad compromise for $15,000 in savings right? They don't like to advertise that the newer model uses many cheaper and inferior components like a plastic lens instead of glass, which makes a huge difference to image quality. There are other differences but this is about Blu Ray players.
In theory, any digital source should look similar because they draw from 1's and 0's that should be the same every time. In practice, some players seem to find more detailed imagery that others from the same source. I don't have the technical expertise to explain exactly why but my belief is that it is in the video processing and what it does to frame smoothness. Anyone with a tv or projector that has frame interpolation, love it or hate it, you can't argue that it does make the image look more detailed. There are a number of things that video processors can do to make content look better and high end Blu Ray players have better built in processing.
If you have a separate processor, or a high end tv or projector with decent processing, you might not need an expensive Blu Ray player as it would just duplicate what you already have. If your tv or projector is entry level and you have no separate processor, you may well experience a noticeable improvement in what you see on-screen with an expensive player. This might include smoother more detail frames with less blur, sharper edges and more vibrant and accurate colors. You may also have more control to manipulate such things to make it to your taste.
It's a shame manufacturers specs have become so useless and misleading. They focus on the parts that people look for like contrast ratios, number of speaker channels and brightness, but rarely enough to help you tell entry level from high performance.
If you have a choice between buying an expensive Blu Ray player with great built in video and sound processing, or buying an entry level player and great outboard processors, the latter would offer better value as the processors will be of use long after we say good night to Blu Ray and every other disc format. Streaming is more convenient and cheaper and, most people like those qualities. CD was better than MP3 but where are they now. If you don't already have a high end Blu Ray player, maybe give it a miss for now. It can't be long before a new format with 4k support is here. ( hopefully not another outdated disc format!). Put your money into an outboard processor and a better projector instead!