While I am far from plateauing in SEO, I find knowledge growth to be the 1 thing that stimulates me more than anything so here is my overall plan (maybe it will help you.)
I went through all the jobs posted online that I would be interested in - SEO, digital marketing, marketing manager, CMO, etc. and pulled out every skill they mention. I saved each one as a unique value so if 3 jobs mentioned "keyword research" I had it in my data 3 times. Then I sorted the table by how often those skills were mentioned. I have focused my education over the last year on the ones that "most" jobs required. When I get tired of studying SEO, I look at things I don't know in PPC or analytics, copywriting, blogging, web design & UX, etc.
I also looked at the "fringe" topics on Inbound (fringe to my knowledge base.) I find those topics that "sort of" relate to what I'm doing and get better. I want to increase my programming knowledge, my database skills and my sales psychology. I don't have to do every job myself but it definitely helps to understand the basics and sometimes the intermediate levels of each.
Some of the skills I have been working on this year from the list: Dashboarding, ROI analysis, PPC, link building, branding, social media strategies, B2B sales, press release writing, Adobe suite, Adsense/Adwords/Analytics, Hootsuite & Twitter tools, WC3, CSS, PHP, eDM, and specifically, I'm studying the FMCG industry because of my limited experience in it and desire to work in that sector one day.
Hope that helps - when I'm bored, I change data sources, as well. I read about 300 blogs in Google Reader, about 50 in Flipboard and I read Inbound.org daily. Between the three, I get a LOT of great stuff to read. I also follow about a billion people on Twitter so I see a lot of new content as it's being released. Just figure out your incoming and change it up a bit if you're bored of it.
~Matt