Allow me to add more fuel to this fire;
Car Seats
Yes, they fit pretty well in the rear seat. However, if your kids are tall then you might start running out of leg room as their legs dangle off the seats. Also, if you're tall and have the seats WAY back...
I have two kids, now aged 5 and 3... and I had an SVX up until about a year or so ago. So I've tried rear-facing and forward-facing seats. The forward-facing fit best by far, and kids rarely complained.
Lots of glass means it will get warm though...
Cruising
This is what the SVX is built for. I drove from St. Louis to Oklahoma City at least three times in an SVX (twice in a 95, once in a 94) and it was by far the most comfortable ride I've ever had. I think for cruising the leather seats are more comfortable than the cloth, but the cloth seats are better in a town-car where you're getting in and out of the car a lot on sunny days. Plus the cockpit is so well laid out and ergonomically perfect imho that it makes driving an absolute pleasure. I used to enjoy nothing more than cruising down the highway at 100 miles per hour for 4 hours straight (shh... don't tell any cops!) with Mozart lilting out of the speakers. Talk about nirvana!
General
The only problem with the SVX is less about kids and more about pregnant wives! My wife found the SVX rather uncomfortable while she was pregnant... she never did figure out exactly why. Also, try to avoid putting anyone over 5'10" in the rear seat for more than 30 minutes... that might be considered unreasonable punishment in some states
Hope this helps!