At-least you can get visitors from those links but only of you comment useful and relevant to articles post.

other than that are there any?

are there any benefits related to SEO that come from spamming wordpress blogs with scrapebox?

No they are not all nofollow..... a lot are but there are plenty that are not.

Any backlinks are great. If you aren't spending alot of effort getting 10k backlinks, then the question is: "why not?"?

Spammy blogs are no good? Not really. Check out some proofs here: PageRank Link Diffusion: Myth or Fact by Terry Kyle

Some say Google will penalized you for linking from spammy blogs or so-called link farms. Try that on the competitor that rank above you instead and see if he'll get lost from the Search Engine

Haruka

You always look for pages with high page rank, are the most benefits cease.
The problem is to find these pages but worth the effort because you'll benefit greatly.
A link one page high page rank you dara good presentation before google.

you can save the failed comments. Then try that list. You will often get a some to stick that didnt inthe first time. Try commenting with or without proxies.
basically i believe that it is you should be methodical with commenting, spin your comments ,sentences and not just one or 2 words.
You should change up your "Anchor Text", good ratio is - 1 anchor text for each 100 comments. .

One last thing..do an "Index" test and clear all non-index results from your list.