Hi lawsio,
Early last year I had a jet black IS220D (unfortunately it's written off now) But during that time I was starting to think that the car was a little too small for me, my wife and two kids, a 6 year old and an 18month old to fit comfortably.
So after I wrote off my black IS220D (long story) I concidered replacing it with all sorts of MPV's SUV's etc for the extra space an economy they offer.
However, after much deliberation guess what car I ended up buying....... yep, another IS220D this time in metalic blue slate,
I really couldn't face having to potentially drive a bus around everyday.
That being said IS220/IS250 as you know isn't the best vehicle to use for transporting a growing family, as there are obviously far better alternatives out there, but in reality at least for me anyway it actually works out fine as our kids are still small.
Once the children have grown an extra few feet in height then maybe It would be wiser to concider opting for a slightly larger vehicle.
But for now if like me you are still enjoying your IS220D, then I would suggest keeping it a while longer or at least until you really need to upsize.
Hope this helps somewhat.