G'day Andy
Sounds like you're going through a similar selection process as us (myself, wife + 2 small kids) at the moment - so I'd be interested to hear how you go....
I think we have considered just about everything available out there in about the <$30k price bracket, and for us, we're leaning towards the DOT 6. I love how light and compact it is, and the great storage which can be easily accessed both when the camper is packed up or when it's set up....and I don't think I've seen a better camp kitchen setup than the Drifta!
We try to do a fair bit of beach camping, and so weight is a major factor in our selection. Just last weekend I was at Main Beach at Straddie, and saw a guy get bogged trying to get up a reasonably simple exit. He was towing a Jayco Freedom pop-top (reckon Tare would have been about 1100-1200kg) with a Landcruiser, got stuck on the exit and couldn't go forwards or reverse. He had to winch up the exit. Admittedly, that could have had a lot to do with incorrect tyre pressures etc - but seeing all that hassle just illustrated to me the importance of trailer weight - and trying to minimise it where possible for the trips we do
The sticking point (for us) with the DOT 6 is definitely the sleeping area in the roof-top tent, and lack of area to get changed. However, I think putting the walls up around the tent awning area (which by watching the videos, simply clips onto the awning and should only take 5 minutes) would provide an area to get changed. In regards to the sleeping area - while the kids are little, I think we could all fit up in the tent. I figure by the time it gets squishy in the tent, one of them will be old enough to roll out a swag in the downstairs area. Maybe sleeping 1 or 2 of your kids in the downstairs area with the walls up could be an option for you??
I also considered the DOT 7 camper like yourself, but kept coming back to the RTT setup because it's off the ground (packing up dirty tents and ground sheets is an annoyance of mine). We've also considered forward-fold hard floors (able to sleep the kids in the converted dining area), but a lot of them are too heavy for me. Another one to consider is Lifestyle's Breakaway....
Anyway, decisions decisions hey! Good luck in the hunt!
Cheers
Matt