I also think it is sometimes hard to know what to say if everyone else who has commented has already said what you want to say. I always struggle with that... do I say what everyone else just said in the comments above? Is that going to look cheesy and like it isn't sincere? Or like Roni said, you might not really be able to put your finger on why you like it, but you think it is great. All such interesting things to think about. I really like to find layouts that don't have any love and leave some so every page might get some attention. Obviously I can't find every one, but if I have time, I like to scroll around just to see what is out there and who might have posted at a busy time and got bumped from the front page and under-appreciated.
This whole digi community is so interesting to me.
I generally try to reciprocate if someone leaves me a comment. Those to me, can sometimes be the hardest because I don't want it to sound like I'm just leaving a comment because they commented on mine. It also blows me away to think that people copy/paste comments. I guess I'd never thought of it before because I don't really hang out in the big galleries, but getting a high post count doesn't seem like a good reason to do that. I generally don't really think about why someone left a comment, but now my mind is just a buzz. LOL.
But I totally understand what you are saying about having your favorite layouts get the *cricket* treatment and others that you don't care about as much get more attention. It is so weird. That is why, when my DD and I were making arts/crafts to sell, we'd always hang on to something we didn't really like so much because we figured that someone might have that be their favorite thing ever.