The baking soda method is a good general method for cleaning odours from anything, however I'd be wary of using the vanilla... sounds like it could leave an undesireable flavouring behind.
Also - if you've ever added baking soda to tea, you'll find it reacts the same way that it does when you add vinegar (I've done it. Don't ask.
). It releases a lot of gas and bubbles like crazy. There's a major chemical reaction between baking soda and brewed tea. Baking soda is also notoriously difficult to rinse away, as it will get into the pores of most materials. Sooo... it's possible that it might not be a good thing to put in your tea tins.
Not sure, but I'd be careful.
Here's a method for cleaning glass pots that I learned a long time ago when I was a waitor in a trashy diner. It should work for tins also (though I haven't tried it).
Rinse the pot with boiling water. Empty it. Dump a teaspoon or two of table salt in the pot. Put about a cup or two of ice cubes in the pot. Sqeeze out a couple lemons wedges into the pot, and then toss the wedges in. Swish around indefinately until your arm gets tired, or the ice melts... whichever comes first. Dump the stuff out. Rinse with hot water again.
I'm not sure what is happening, chemically speaking, exactly.. But it cleans the grimy brown deposit from the bottom of those pots like nothing else, and removes (and doesn't leave) any odour.
Give it a try on your tins, and see what happens!
Hope that helps,