This is true, but I also recall testing it at the relevant speeds--around 1/15-1/60 sec.--and it didn't make a difference for me. There are other factors like the condition of the camera and the tripod system that could also be important.
As for in-camera spot metering, indeed, you've got to be careful where you point the spot, but eventually you can get in the habit of thinking where you want to place the exposure, metering, setting the exposure, and composing. I don't usually find it necessary to meter every shot. If there's a situation like moving clouds, I might have one setting for full sun and one for cloud cover or one for sun and one for shade, and then I can meter again if something else arises, and I get more consistent results than I would in any kind of auto mode or otherwise adjusting exposure for every shot.