I haven't used LitMatch, but I love AgentQuery. So long as an agent reference list isn't showcasing scam artists, I think they are extremely valuable.
Yes, their proper use is as a sorting device and springboard to further research. Sure, some writers will impatiently use the info "as is" instead of looking further. But the value they provide to the writers who use them properly far outweighs the potential for some extra, inappropriate queries making their way across an agent's desk. Of course, this is my writer's pov coming through--obviously those extra queries are a serious problem to Mr Zack.
His frustration with queries that continue to flow even after he has shut down to accepting them temporarily or changed his address is certainly concerning--much like trying to get something fixed on one's credit rating, and the credit organizations keep quoting each other, over-riding the individual attempts to correct.
And if Elodie's flippant comment that she is "too busy" to go "hunting high and low" for agent addresses is anything to go by, there are plenty of writers who think visiting an agent website for specifics is too much trouble. This is something I can't understand, but I accept that it exists. No wonder Mr Zack is annoyed. (Elodie, I don't mean this as an attack--I'm just honestly flummoxed by that point of view. Perhaps you were exagerating for humorous effect. Or perhaps I misunderstood what you meant. You said addresses, which I assume to mean mailing addresses. Do you really take them off the reference site without double checking the agent's own? Or did you mean web addresses, as a first step to more research?)
From the perspective of a writer who used such a reference site as a valuable first step to finding an agent, I don't see what the alternative is. How is a writer of urban or Tolkienesque fantasy, for example, to know to look at Mr Zack's website, without some form of reference telling him or her that Mr Zack is an agent and, generally, what he represents? As others have pointed out, both printed references and online ones have the trouble of going out-of-date. Mr Zack, is your proposal that all references should be boycotted/avoided, or that there should be one or two centralized ones only?
Also, Mr Zack, you said that an agent's preference for only showcasing their latest sales should be respected. I respectfully disagree. An agent's history of past sales is important for a writer to know when evaluating whether someone is the right agent for them.