In poor visibility - e.g. LVPs - final approach separation will be greatly increased. It may also be increased for other weather factors - wind, rain, snow, etc. The spacing is decided by the Tower and implemented by Approach Control.
ATC will usually instigate a go-around for traffic reasons and most pilots will keep coming.... I have never seen a go-around instigated by a pilot for traffic reasons although I'm sure it must happen..