geekgirl in a way I can understand your dh's frustration if he feels he can provide a better standard of living for his family in Germany. Having a bigger, better built home would contribute to your whole quality of life but it wouldn't compensate for worrying about your dd's school-life.
I doubt very much that the seperation of dc with SN into Sonderschulen is intended to be in any way unfair to those families. The logic behind it I think lies in the German tradition of specialised professional training. A Sonderschullehrer has been through a specialist course and is therefore qualified to teach dc with SN. A teacher within the ordinary state system has not been exposed to this training so would feel unqualified to attempt it. I could well imagine that Sonderschulen would be located in "nice" areas and with better facilities than the other schools.
There is a hearing/seeing impaired school near my dd's and we used their swimming pool once. It's the only school I have come across here with its own pool for instance.
I think you would need to go and have a good look around the Sonderschulen that your dd might attend and try hard to get a feeling for the place. What might be good for you is having contact to families who are experiencing similar situations to you and will understand you. What I find a little sad is that in your current school/community your dd belongs and is accepted. It would be very difficult for me to give that up too in your place.
It will depend a lot too on where in Germany you were to settle. You know yourself that someone living in the centre of Glasgow will make very different experiences to someone living say in Devon.
I think that the German govt does try to make a lot available to help families with a SN dc. There are family Kuren, organisations which organise holidays and so on and many other clubs/Vereine.
My dd goes horse riding here for instance:
www.reitsportverein-maifeld.de/angebot.htm
scroll down to the bottom where it explains how they work with the disabled , if you can read German