When reviewing query letters on Query Shark, I very rarely see mention of why the particular agent has been selected. Is this omitted from your post or is it not necessary to include?
One of the disadvantages to QueryShark is that my preferences on some things are not the universal. Clearly this is a cosmic error of epic proportion and will be remedied when I am Queen of the Known Universe.
However, while we wait for that happy day, personalized queries are largely seen as A Good Thing by most agents. Not me. I'm an agent. You're a writer. I have skills you need. You have a good project I might want to sell. As Robert Parker so memorably said in an early Spenser novel "Enough with the love talk, off with the clothes."
And frankly, personalization is just one more hoop writers are asked to jump through for no good reason. It doesn't improve the quality of your writing. It doesn't help me evaluate your work. Basically it's a fucking ego stroke for agents and I have zero tolerance for that as a prerequisite for paying attention to a query.
IF you say you read Sean Ferrell's Man in the Empty Suit and loved it with the passion of a white hot sun, yes, that's something I pay attention to. So, even my ice cold heart can be melted with some sincere personalization. (Notice it's not about ME, it's about one of the Fabulosity---that's a big thing to remember.)
IF you say you've read Josin McQuein's Premeditated and loved it with the passion of a white hot sun and you're querying with your YA novel, that shows me you are NOT paying attention, cause I don't rep Josin, and didn't sell the book. I was just her first fan (of MANY.)
That's the very real downside of personalization---you have to really pay attention to details. And that's the reason I think it's shortsighted to ask writers to do this. Why should you have to research this kind of detail for agents at the query stage? Your time is more valuable than that. Unless you're writing the definitive history of Sharques in the Marketplace, who cares that I found Josin in the QueryShark chums?
But I've been on enough panels with other agents and heard them say they like to know why an author is querying to know I'm probably in the minority on this.
The good thing though is that so many agents are so much more visible and accessible now it makes it easier to find something good to say.
And while agents may like it, I don't think any agent anywhere at any time is going to reject a query because it doesn't contain the reason you're writing to them. We're all looking for good stuff to sell. Tell us about the book in an enticing way and don't fret about anything else.