The price for LR3's at the 10 year mark is making them extremely attractive trucks for a lot of reasons. My personal opinion is that you are getting way more truck for the $ than in many of the previous Discovery generations (even with my bias towards D1's, my LR3/D3 is just a better vehicle across the board when it comes to DD duties).
I'll be interested in Jjmmiejamz or one of the other folks with more time on them at the dealership has to say about the transmissions; if I was laying down odds I'd say you are seeing warrenty replacement work. My understanding is that the drivetrain of the 4.4L is great until you get to the difs and there is where there have been some issues but what is worth noting is 'some issues' is not equivical to 'Dii head gaskets also had some issues' or 'P38's' Meaning the 3 is a vastly better platform reliability wise.
As a DD/kid hauler they are superb. The seven seater is nice if you want to be able to seperate the savages, the way the seats all fold flat provides excellent storage space for those bed, bath, & beyond trips. Comfort on the road is excellent too.
For the 10yr olds entering the market now you should def look for service interval. You should also expect to see an EAS compressor replacement or budget accordingly. As you have probably read these things eat brakes, bushings, and tires due to their weight so also look to see when the lower control arms were done and such.
Still, I'd suggest some test drives, I don't think the better half will be disappointed in the 3.
r-
Ray