I agree completely re: a lot of good comments getting pushed down. The new comment boosting option from MinnowBooster is not going to help in the comment spam regard, but that's another topic for another day.
One thing I will point out though...if you think it's bad now, wait until the platform grows, with 1, 2, even 10 million users. What will the comment spam look like then? It's a problem whicih won't go away.
I think it'll need addressing in the same way traditional (pre-Steemit) bloggers have done - and many turned off comments altogether.