I think it's fine to let replying get away from you every once in a while, you know? We all have a life, so I'm sure people understand. It's clear for followers when you're someone who never responds or just going through something, so don't be too hard on yourself! :D
I think it's nice to respond too, it's just common courtesy really, even if it's a small "thanks". And I agree, comments have brought serious surprises to me down the years with some earning more than some posts, so definitely worth a shot if you're looking to earn a bit as a newbie.
Yes fair play I'm not letting it bother me that much, I will get around to responding to the backlog eventually though, just need to find 30 mins or so!
And yes there are those who never respond, that's just rude!