I come to HN for the comments. Every now and then I'll read something that really inspires me. I'm not necessarily talking about great advice, either. Sometimes just reading over other people's frustrations will lead me to new business ideas.
The supposed decline in submission quality is mostly an illusion. PG set up a page that only shows submissions by older users (first six months or first year --not sure which) to evaluate the supposed submission quality decline:
http://news.ycombinator.com/classic
Additionally, everything has an item ID #, so if you want to prove it to yourself, you can go through everything sequentially.
There's 3 things I think are affecting the quality:
1) A lot of stuff is written specifically targeting HN, that probably didn't happen when the traffic a front page story got was negligible
2) There are sites that blindly submit everything they publish
3) There are people who blindly submit popular sites within seconds of them publishing anything
You don't have to be a new account to be doing any of those things. My account's ~4 years old, I could be doing any or all of them.