I am interested to follow peoples thoughts on this.
Some logistical comments:
We visited in 2003 (I think?) for Remembrance day, and have done the Anzac day services there in 2008 and 2011. For all of those trips, we either stayed in Amiens or in Glisy, which is on the outskirts of Amiens, towards Villers-Bretonneux. We have always had a car. For the two dawn services, we were able to drive up and park on the road that the Australian memorial is on. I know that's no longer possible for the dawn service, and I believe you must park in Villers-Bretonneux or Fouilloy, and walk from there.
I guess much like attending a service at Gallipoli vs visiting there when it's not bombarded by tourists - what is of interest to you? We are interested in the service aspect, as well as toodling around the area (the 2008 trip we spent another 2-3 days visiting every cemetery in the Somme - OK, not exactly, but it felt like it to our 18 month old!!). If you are not so interested in the service, then visiting at another time is perfect.
Based on what I observed in 2008 and 2011, the area around the memorial is extra busy with visitors the day before, but they tend to leave by mid-morning/lunch time on the 25th. A number of people being on tours helps a bit with that - have to get on the bus to the next stop in the tour. Immediately after the service, there are some crowds, but they do tend to dissipate, and you can get closer to the memorial and find spots to be quiet and take in the sense of place and atmosphere. The services I've been to felt like some of the larger, local services you would find in Australia, but with some French speeches, the French anthem, and the ability to be seated! Handy when the temperature drops down further before dawn.
Next year may be different with the opening of the Monash centre around the back of the memorial.
Another option to consider for those who are interested - though it's likely to be much colder - is the services in the area on 11 November for 100 years since Armistice.
(I wasn't sure where to put this post, so I picked Destination Guide??!!)