I tried to sum up all of the suggestions around the tour problem so here's the suggestion.

A tour section should be added where you could create or modify a tour.

Tour info would not be added when you add a new setlist but be defined by a range of dates.

eg. "Tour #1 from 08-10-2008 to 12-12-2008"
or "Tour #2 from 01-01-2009 to 02-02-09 and continues from 03-03-2009 to 04-04-2009" (this would allow a break in the tour to support another band for exemple)

We could also add legs for each tour which would be interesting to separate for average setlists for exemple
eg. Metallica's World Magnetic Tour has Euro, US, Japanese, etc. legs

Finally, we could add something like this :

Tour #1
Show #1 setlist available
Show #2 setlist missing!
Show #3 setlist available
...

It would motivate people to help completing I guess.

Hope you like it.