I get the concern generally, but why would someone bother to pull the whois information and email you when they could have simply typed in the name to a browser and gotten your landing page? Or searched for the name in any of the large marketplaces that would include the affiliates? I've never gotten anything but bullshit from those emails. All that said, everyone should be able to make the choice. Personally I stopped replying to any of them long before GoDaddy shut it off.
Yes, it's understandable that it may not be worth the hassle to get those emails. And, no doubt GD had some feedback, when spam was extremely rampant, that customers wanted the spam to stop, ergo perhaps this drastic solution.
But, consider the benefit potentially of those few cherished buyers that do come to you.
save generally 10-20% currently with the marketplaces --- unless using you use your own customized landers.
-- email is fast, with no go between. And the domain owner who is a negotiation pro can work his or her magic directly
- the potential buyer is a lead, with potential for other sales. Do you really want to share that lead with others?
-- For the buyer, they are not faced with additional potential upselling. This includes being required to renew the domain even if it is not even close to expiration. A sale could be lost at that point, when the price starts going up higher than you posted.
Or, by being redirected to a broker, they could be sold a different, more expensive alternative. And you might not even know that your lander was used as a "bait and switch."
-- you don't have to worry about losing a potential customer that doesn't want to deal with some third-party lander or broker.
And it really is important to be reminded that some potential end-users may be far more comfortable directly dealing with the owner. It's a matter of choice you are also honoring, if that's what they would prefer.