From a newcomers perspectiveLike all good old timers no one likes change, yet there's always that new generation coming leading the way and taking the jump. For some, caught up with their habits, change seems daunting, but I believe it's unavoidable, so minds will get it done sooner!
I see it as follows: theirs 2 main happenings on the forum. Deals and discussions / advice / debates and shmoozing.
For the deals aspect (which for many users is thier main presence), a reimagined sight is definitely necessary going forward. In an age where phones are becoming the only device a person owns, to instant notifications and blazing internet speeds, getting that deal, -and clearly marked as a deal- is essential and every second counts. I would say that's a priority and should be dealt with first, with two key points.
1. When posting a deal it should be highlighted in the thread and have separate notification options. (That allows for a deal and discussion type of thread to take place in harmony
example) 2. The process like DDMS, should be done gradually and smartly.
Then there's the discussions / advice / debates and shmoozing, the importance of the longtime members along with the less of a necessity for notification speed, would leave this category with strongest need for time and user-familiarity. Meaning wait till users get comfortable with the design and layout, before even starting to migrate. For this I would say, focus more on the way it was and less on better organization, leading the user to get lost (at least in the beginning).
In short: a combination of "redoing the entire site" and "make a new deal only site", in a manner that gives encouragement to join, while keeping all users happy:)
One of my favorite forum designs (except the ads)
https://www.xda-developers.com/Edit:
An idea to encourage reading new threads, have a random / popular thread of the day.
In the beginning, understanding the whole Amazon / Walmart deals threads was quite the learning curve, understanding how a first timer approaches the forum can go a long way to growth in users and usage!