Even if this turns out to be another disappointing release (if there's any at all), at least there are...alternative sources for high res scans of the theatrical cuts.
Not benefits worth the effort. Outside of gaming, which renders natively at the resolution chosen, 4K is mostly a scam, really. Unless you're doing full restoration from high quality film prints of a film with no CG in it (or else re-rendering the CG at 4K), you're pretty much wasting your time.
Not necessarily. 4k Blu-ray has a wider color space using DCI-P3 (and someday Rec. 2020). This is the same color space used for D-Cinema and better than Rec. 709 on regular Blu-ray. There's also HDR, as well as the immersive audio formats (e.g. Dolby Atmos and DTS: X) too. Resolution is only a component of 4k Blu-ray and current UHD standards.
Even still, while the resolution may not appear to be dramatically higher, there's still a benefit to a 2k master on 4k Blu-ray too. D-Cinema 2k is technically a higher res than 1080p and a 4k Blu-ray from a 2k master can still sometimes show a little bit more detail. There are screencaps that show this with the Martian, for example.
Whether or not any of this it's enough of a difference to you is a fair argument to make. It certainly costs a lot right now and the tech is still pretty new. All the kinks have yet to be worked out. I wouldn't call it a scam though.