Whilst I think it would be nice to spread the test matches across the country, what the locals in the South Island are really missing out on is the atmosphere of having the Lions in town - but then again, they'll still be visiting for the midweek matches anyway.
If we were to arbitrarily decide that 25% of the population wanted to attend a test match, that would mean roughly 300,000 people in Auckland and 30,000 people in Dunedin want to go along.
If 60,000 people attend in Auckland, that still leaves 240,000 people missing out (or 80%). In contrast, if 30,000 people attend in Dunedin, no one misses out.
Of course the numbers above are arbitrary, and you could argue that Dunedinites are more likely to go to a match than Aucklanders (though the fact that Highlanders games were sold out and Blues games weren't is irrelevant, because obviously more people attend matches when a team is winning), but I think it would be wrong to suggest that people in Otago are missing out if Auckland gets two test matches because, at the end of the day, a lot more people are going to miss out in Auckland regardless.