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Stack the best ones at the end, and link into those in series as it makes sense for the user. The lower end directory pages support the best ones in your hub.
As others have mentioned, I use these to create my own authority hub.
Building quality inbound links to those articles then helps fuels the entire hub.
Others have added the idea of using relevant profile listings to link to articles at various steps in the process, and using social bookmarking to enhance it all.
Difficult to say 'where' it crosses the line. I would suggest as long as it provides real value, its valuable to do :)