The solution to this is to create a public user action that only returns the value a site property, and is consumed by other espaces.
Although, if site properties could be made public, that way it would be easier to share site properties among espaces.

Good suggestion.

@Tiago, yes, but the problem with that is, you have to republish the consumers espace when a site-property is updated.
because the property is cached in the consumers-espace.
which imho, is not correct!

Maybe you could store the properity into a database table and enable caching on the query.

Get the information from the database, use it in any eSpace you wish.

Joost,
Don't know exactly what you mean when you say you have to republish the consumer espace when the site property is updated.
In 5.1 tried the following test, and it works ok, as I expected:
1-Consumer espace consumes action that returns the value of a site property.
2-In consumer espace displayed the current value of the site property. Ok.
3-In producer espace updated the value of the site property.
4-In consumer espace displayed the current value of the site property. Ok, displayed the new value.
No republication was needed of the consumer espaces.

Good suggestion. @Tiago, yes, but the problem with that is, you have to republish the consumers espace when a site-property is updated. because the property is cached in the consumers-espace. which imho, is not correct!