doeweb - First off, the price difference is $200.00. Now to answer your question: Yes and no.
If you are one of those who demand exactness, then yes, the digital PID controller is worth the extra money. Properly set, it will hold the temp to within a couple of degrees of your set point. And it will allow you to cook to a desired internal temp. And you can program it to go to a keep warm setting after the meat reaches the desired internal temp. The D units have a 3 year warranty except for the PID controller which is warranted for 1 year.
If you can live with temperature swings of 20 or so degrees higher than your set point and the same below your set point as the smoker cycles on and off. then no, you do not need the PID. Just a good remote like a Maverick or a ThermaQ for monitoring smoker temp and meat temp. The analog units are very robust and reliably simple. These units have a full 3 year warranty on the entire unit.
If something like ribs are going to need 5.30 hours to smoke and be off the bone tender, it matters not whether there are temp swings or PID accuracy. 5.30 hours is the same no matter what. Now it is mostly a matter of preference. Your furnace, AC, oven all cycle on and off to maintain the set temp. They may cycle for several minutes at a time. With the PID, the cycling is rapid since there is no major over shoot or undershoot.
Now, for the price of the 2D, you can get the analog 3, a larger unit. Later on, if you want to, you can buy an Auber unit for the smoker. Just something to think about. No matter what you choose, you are getting a smoker that provides a lot of bang for the money. And do visit the SI site and read up on the units. You can also call the owner, Steve, and ask questions or if you have any concerns. Dave