Psyringe: If your budget allows, then I'd always recommend taking 8 GB over 4 GB, yes. Though with regard to Skyrim Performance, getting a better CPU would probably have a more noticeable effect.
PenutBrittle: Skyrim is a 32 bit program which makes 4GB of ram the absolute maximum it can use, after the latest patch. Of course, more ram is better for other things, but it won't make a tiny difference for Skyrim in particular.
It will make a difference when you run something else at the same time - for example, a browser with a couple of windows open (browsers have become excessively memory hungry during the last years). Windows and the programs in your tray need some memory too. This is not an unusual usage scenario imho. Also, when you're sure that none of your programs will access the whole memory, you can turn part of it into a ramdisk for access times that run circles around SSDs.
But you'r correct that Skyrim will never use more than 4 GB by itself. I just think that there are realistic usage scenarios that make the whole machine run noticeably faster with 8 GB nevertheless. Which is why I recommended that memory upgrade as a non-essential, but useful addition. But as I said, the effect of upgrading the CPU will be more noticeable.
