Hi Chris,
These are great ideas and we are in the process of looking at how we can improve our search so these are really useful. We particularly love the one about an image being flagged if it is in a Tour so people can discover great content as they browse the site.
I am not sure if this is what you were referring to, but there is a way to search users on the site via the Channel search (this is also available on the iPhone app):
http://www.historypin.com/channels/However you can't yet search for a tour which we exploring.
And you can get a link to your Tour/Collection when Tour on your Channel, so you can drop it into places for people to click on.
http://www.historypin.com/channels/view/id/16280134/#|tours/view/id/18373104/title/Waterfront%20at%20WarHope that helps a little , do keep us posted on other features you would find useful.
Rebekkah