I know my story is good. I believe my characters are strong. But I admit I'm a novice and could improve a lot--and have much to learn.
But not a single response to 20 query letters mailed 6 weeks ago? How many more before I decide to abandon this silly dream?
Keeping working on your next project, sure, but don't stop sending on this one. So you're a novice. You could be a really, really good novice for all I know. I say query until your agent list is exhausted. Also note there are a few agencies who are perfectly fine with you querying another agent at that same agency after one has passed.
It's important to know that silence is considered the form rejection of queries. The query that came close to a request gets the same non-reply as the one that's barely in coherent English. I actually get a bit excited when I see a reply to a query because there's decent odds that it's a request. (Not great odds, mind you, but decent.)
I think some queries do well with a hook and others don't. I think if you're going to use one, it should feel essential, like the query would sound really weird without the hook there.
SYW is an amazing place to get feedback on queries, but it's not the only tool. One exercise that helped me* was pretending to be an agent. I printed out twenty query letters (from AW and similar boards) and read each one until I either finished or lost interest. When I did lose interest, I noted why. I set aside the ones I would ask for pages from. A lot of queries weren't bad. They just blended in with the crowd too much. Then, when I went back to my query, I had a much stronger handle on what parts made it feel unique and what parts made it feel like every other query out there. Maybe the same exercise would work for you.
Good luck!
*When I say "helped", I mean I got a better feel for how to write queries, not "hey, I got an agent and my book sold instantly and now everyone loves me." Though that would've been cool.