This has been suggested multiple times by various reasons. The reason guardoans don't spawn very often is because Towny is set to the Easy difficulty while Wild is set to the Hard difficulty. Now making a guardian farm in wild is too risky because who knows when you get griefed.
It is true that Guardians and Iron golems do not introduce any meebles to the economy, however as an economy person I can say that they introduce items to the economy which lowers the value of that item, resulting a never ending deflation.
I am not in favor of this personally, but you may need to change your suggestion to setting the difficulty to Hard.