Wouldn't all this depend on your target customers? If your target customer is big business that have fast computers you are okay.

If your customers are average joes, then yes I would say you should have a test environment in place that closely represents those customers.

Even after all that the question I have is which set of customers brings in the most money for you? Lets say you have a mix of big business that run fast machines, and average joes that run slow machines. If 90% of your money comes from big business, why bother trying to make software for the slow machines? Just slap on a system requirement and it should cover them, so-to-speak.