"Incredulous" and "plausible" are both relative terms, which can only ever be based on believe. Eg science books, school, television, etc. I will point out that science books are re-written with each generation, and it's really not uncommon that new discoveries require that old paradigms be thrown in the garbage occasionally.
We're doing the exact same thing with Einstein's relativity right now, as GPS has proven it to be nonsense.
As for the 3d image, yes of course I've looked at it. I'm not really sure what your point is though? I can see very clear elevation relative to the shape of a mushroom, especially the tip and the base of the cap. It looks exactly what I'd expect a partially buried mushroom cap to look like.
"but had you found something similar which vaguely resembled the shape of a boat, would you have suspected it to be a gigantic stone age craft of some sort?" -
Let's be honest please, it's not a "vague shape", it is a VERY high resolution image akin to looking at a specimen under a microscope. There is an enormous amount of detail and structure here (there is a hole in the ground below it's stem and it's even possible to see underneath the cap), so from a scientific point of view it would be unreasonable to suggest that this amount of detail and structure is somehow random. Especially considering the 'huge dead forest' theme of the surrounding area...
I understand your desire to dismiss this find as random pixels/glitch/spare sand and so let me add this assumed caveat "assuming that this is what it looks like..." what exactly can be learned from it?
How specifically does this specimen differ from modern mushrooms? Is there a modern parallel to the round structures that can be seen under the cap? Is there a modern parallel to this specimen?