Hi Mokkyukkyu,
Thanks for the question! The short answer is that I would definitely upgrade to the newest version. The differences between the 2008 and 2016 versions are vast, and the 2016 version is far more comprehensive. So, if you do upgrade, I would stop using the 2008 version and use just the 2016 version (the 2016 version includes all of the info in the 2008 version, and then much much more).
Ok, with the short answer out of the way, let me give you some additional info on the differences. Since I've been asked this question in the past, I've written about it on our blog several times, so I'll link those articles here, and then add a short summary. This should give you a better sense of the scope of the changes since 2008.
First, here's a general discussion of why I change the Bibles each year:
The 2016 LSAT Bibles: Do You Need the Newest Editions? Part I. Most relevant to you, this explains how I track changes in the LSAT and then make changes in the text of the books, and that I do the same for the questions students ask (which helps the book get clearer and easier to use each year)
Next, in this article I discuss the changes in each Bible over the years:
The 2016 LSAT Bibles: Do You Need the Newest Editions? Part II. The LGB is the first book covered there, and the 2008 version was about 416 pages whereas the 2016 version is around 700 pages. So, the newer edition has almost
300 more pages, and within those pages are a lot of useful tips and strategies. As I discuss within the article, the changes over time included "new, refined, and expanded discussions of many critical Logic Games concepts, expanded discussions of question types and solution strategies, multiple new and expanded drills, added and changed LSAT Logic Games, a glossary/index which defines each term in the book, and a ReChallenge section dividing all of the games in the book into Challenge sections. There was even multiple upgrades to the book website, where we ultimately presented dozens of pages of supplementary drills and online presentations on challenging concepts and questions for free."
Last, I'll link two of the articles I've posted showing some of the individual changes from year to year.
I think that should explain in depth why I believe that getting the 2016 version would be a big help to you. I'm generally quite sensitive to the cost of these books, and so I don't just make a blanket recommendation to always get the newest version when ask about upgrading. However, in your case,t he 2008 version is so different that I feel that you would be missing to on a lot if valuable information if you did not upgrade. So, that's my recommendation here
Please let me know if that helps, and if you have any additional questions that i can help out with. Thanks!