Circl+
What upgrading a space changes.
A space can have Circl+. It is a property of the space, not of a person, so upgrading one does not change anything in your other spaces.
What it adds
The clearest difference is the accent colour. A space with Circl+ can use its own colour throughout the app rather than the standard green, picked from a set of presets. It makes several spaces easier to tell apart at a glance.
What it does not change
Circl+ does not affect location accuracy, notifications, places, moments, or who can see what. A space with one member and a space with ten behave the same way whether or not either has Circl+.
In a space without it
The theme picker shows as unavailable and the space uses the standard green. Nothing else is withheld.