Hi,

to be useful, a value needs to be understood by everyone = other mappers, the people who create maps with the osm data, the people who create gps softwares or any other types of software.

In the wiki, it is written that we can use what we want, that every mapper is free to add any informations.

It is true but if you are the only one  using a value, nobody will see/understand it.

And if you look at https://taginfo.openstreetmap.org/tags/natural=spur#overview, you will see that the 2 values spur was used only by you (zero now because I removed it).

You are right when you say it is possible to use a tag place and a tag natural on the same node.

So I will suggest, if you look at the wiki, part geology related https://wiki.openstreetmap.org/wiki/Key:natural#Geology_related, to try to find something more common, like peak or hill or rock or stone, if needed.

Best regards