Answer 1

I've heard cases of nutjobs spamming SL with 50+ emails in a row. If they get that adding to the normal traffic per day, it's not hard to see why they can't possibly respond to each and every one of the mails they get.
To be fair though, I usually get response within 24 hours, if I am expecting one. For suggestions and heads up about what's going on in SL, I'm not usually expecting replies so that's fine for me.
Have you tried using the in-app feedback feature? Some have claimed that they receive replies faster that way.

Answer 2

I have got a quick reply within 1-2 days the only time that I emailed them about 18 months ago. I haven't emailed them lately.