well as for supoer metroid, it does give quite a good indication of where secrets are, like cthomlan mentioned above, but also there are sometimes rooms that lead to nowhere, no other doors, and then you know something has to be here, they wont make the room for nothing
but the xray defently had its uses to see how to get past certain blockages, is it shine spark, or powerbomb or super missle or just normal bombs, the xray helped with that a low
as for metroid prime 1, i love it i think its one of the few 2D platformer games that actualy did well in 3D, the Scan visor is indeed a bit annoying you spend scanning every room after you clear it. and those names like radion en denzium dont tell you much so you indeed had to look tru your log book. but still i liked the game a lot
a thing i realy loved about the scan vizor was that you could get information about lore, find out useless information about lifeforms and plants, even if it wasnt combat info it greatly increased the feeling of beeying there on an unknown planet far away