If it's the Database Developer world you seek, I agree... a lot has changed. But even more has not and your previous skills will serve you well.

My recommendation would be that you Google for the engine differences between 2000 and 2005 and then learn those. There were some fantastic changes in that jump including some remarkable tools known as "Windowing Functions" and, if you're into it, some great additions for handling (ugh!) XML. They also introduced CTE's (like moving derived tables in FROM clauses up to the top, to be brief) and much more. It would also be a good idea to look into the new "Dynamic Management Views" that replace what used to be done using system tables.

The jump from 2005 to 2008 wasn't quite as climatic programming wise. I skipped it and the 2008R2 version.

Once they got 2012 right (took them 'til sp3), it's freaking awesome. Some of the improvements to SSMS are things that I always thought should be there since the git when it comes to editing.

2014 had more improvements but I'm skipping that.

After being way behind, we finally upgraded from 2005 to 2012 this year. We never live on the bleeding edge so we won't make the jump to 2016 until mid to late 2017.

Also, certifications can help your study patterns and your ability to "get your foot in the door" but they won't help you with the "Ninja" stuff. For example, do you know what a Tally or Numbers Table is an how it can be used to replace certain types of explicit loops in a set-based manner? That's the type of stuff that you won't find in certification books.