In short, if you don't need the space, hide system files again and ignore it.
$RECYCLE.BIN is your, erm, recycle bin for that drive, so anything which is in your recycle bin for this drive is stored in this folder until you empty your recycle bin or it becomes full and starts removing items itself.
msdownld.tmp is a folder used in installations and I've never had a problem removing it.
System Volume Information is, I believe, where system restore data is stored, so if space is tight or you've no intention of ever using system restore (never know when you might need it - unless you maintain your own regular backups) you can disable System Restore for that drive (System > Advanced > System Protection).