Generally speaking, since response times and expected peak requests are usually defined in advance upgrading for speed will only happen if current hardware cant meet the requirements.

It's not really a "bring more value" thing, the customer will either have a clear target throughtput figure or we'll work one out together that satisfies what they want to do (usually trying to make it as low as possible because fast hardware = money) and then it's just a question of whether the current hardware is enough or not.