As others have pointed out, your question's premise is inherently flawed because you are begging the question. Any proposed answer could be considered a self-fulfilling prophecy. Here's a more logical way to think about how to get to a cost-effective test suite.

Creating an automated test suite after-the-fact is difficult for a number of reasons, primarily because a well tuned and effective test suite requires constant feedback to determine what works and what doesn't. You can't get that unless you have adopted a "pay as you go" model where your test feedback influences your codebase and vice versa.

By Michael Feathers' definition, a legacy codebase is one without a test suite. I highly recommend you take a look at his book on the topic. http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052/

If you're interested in the most effective way to maintain your legacy code base, you'll build in the appropriate level of testing (including supporting code, infrastructure, etc.) and force yourself to refactor the parts of it that need to be refactored to support testablity. It will drive out the tests for you that do provide value, and steer you away from lines of thought that do not help you catch regressions or drive refactoring. It gets you to "pay as you go." Not only will this provide you the best argument for management to give you time to write tests, it is the most professionally responsible one as well.

Speaking of professionalism, have a look at Bob Martin's arguments for software craftsmanship and the ethical responsibility software developers have to produce quality work. This might help form your opinion on when and why software quality is important to professional responsibility. There are more to ethics than just the bottom line.

You have to admit, it's sad that this is the approach their legal team is taking. In that respect, it makes Blizzard look a bit lazy -- I mean, who actually drudges through the mid/lower levels of this game and doesn't get the idea to write a bot to do the dirty work? Isn't that what computers are for, anyway? They had to see this coming, right? And this was Blizzard's contingency plan -- to sick their lawyers on people? That's what strikes me as lame about the whole thing.

If you want to make a drug analogy, then do so the right way -- killing demand is the way to truly solve the problem. Not killing supply. A better analogy for this whole situation are bid sniping tools for eBay -- what Blizzard really wants is for things to be fair for paying patrons of their service. If there's enough demand here for a Glide bot, though, maybe they should rethink the design of the game. What are the elements in the game would create demand for such a bot? What are ways around that?

With most games, this whole concept is completely nonsensical, but their game's design does make a very compelling argument for these types of programs. It's why I stopped playing -- and not that anyone still playing WoW cares, but there are a lot of people who stopped playing for the same reason. The burden here is on Blizzard and other successful MMO game developers, and as someone who freely and openly stopped playing WoW for this very reason, I can tell you that I honestly think that Glide/farm bots are a good thing for Blizzard and MMO -- they'll force designers to come up with better games in the end.

Blizzard would do well to learn from this in the future and keep their legal wolves at bay. It's getting old, people go to lawyers to help them "protect" their interests, and all the lawyers do is use scare tactics and set these confusing, logic devoid precedents to sway public opinion and create fear to do anything creative. Isn't that the exact opposite intent of a copyright?