I don't think it's harder Dave probably just less personal, I've only been here a very short while and have noticed that although loads of members use the panda part of the site, a much smaller number use it regularly i.e. most days.
If somebody wants something for the panda a quick post saying such and if anyone can help, they jump straight in without hesitation and mostly free so it wouldn't be advertised in the first place.
The problem with such a large site is that the classifieds are spread amongst a huge membership and I'm sure wanted articles for a specific model get lost amongst the amount of others. This is no critisism in any way shape or form as i think the site is excellent and due to it's size you must be very dedicated with the other moderators in the day to day running.
The classified section in my site in comparison is easy as it is a specialised site for a particular model and almost all classified ads are for that model so you don't have to look long to find all, we only have 170 members as well so the day to day running is again probably much easier in comparison.
A site of this size I think would suit having a classified section for each model you specialise in or even just a sticky wanted post for each section for people to stick a quick post up of something they desperately need and remove it after 7 days or so but it will add more work to regulate