Pinning is reserved for official notices, and -rarely!- for permanently relevant reference topics.
Topics should not be pinned simply because they are interesting.
Such topics can be 'bumped' of 'recommended' as staff pick but not pinned.
If you recommend a topic, please make sure that it is taken down after ~2 weeks.
This guidance is current policy and was affirmed a number of times at management meetings, but obviously the issue is open for discussion here.
I think a case can be made that the price watch should be pinned, in that it is more than interesting, it is useful. I've not discussed it with him yet.