it is possibly a combination of both - long exposures do give you saturated colors. anyone who has used nd400 or nd110 would probably attest to that. but at such extremes even if the filter is neutral, you get some form of ir/uv contamination. i'm not sure which one, i think it is ir.. so you tend to warm the image up a wee bit if you use the "correct wb".. and if you leave it to auto, then it depends on the camera lor.
as for whether nd filter is neutral, not very important i guess, color can always be adjusted.
i like #2 the most here, nice textures in the foreground. i am wondering if you really needed to use gnd (you did, right?) here though. the reflections are brighter than the sky. as a general rule of thumb, unless there is exceptional lighting, equal brightness or darker reflections are expected from landscapes..
i do not share the common sentiment about #3 though, the rocks blending with the horizon (which could have been resolved with a higher perspective to separate them), the 50-50 which doesn't quite seem to work, you need exceptional sky + exceptional foreground to do such.. either that or exceptional mood so that one can overlook the centred horizon.. none of which really applies here. there is also a slight magenta cast on the rocks which can be easily corrected.
same for the coral shot (#4). you might consider a 6x7 , 7x6 or square crop here.. i visualised it, i think the use of space in such a crop is far more efficient.
i do like #5 actually, there is a weird appeal about it.
as for #6, #7 and #1, i have to be honest that the composition just doesn't click for me.