Hello Nigel,
This is a great area to visit, we stayed at Les Trois Chateaux in Eguisheim and highly recommend it. You can walk in to the village in less than 10 minutes and it is a fantastic place, almost like a Disney set, but it is a working village. It is well placed to visit Colmar and also Freiburg and is centrally placed for the wine route. The Vosge mountains are steep, but the roads are generally quite good.
The road from Nancy to Colmar are general very good and should not present any problems to you. If you stop in Nancy use Campeole Le Brabois, there is a bus stop just outside to take you in to the centre. The site is a bit bumpy, but if you have a good look before pitching you should be OK.
Just a thought if you are thinking of going in September, have a look at my post on Events and rallies about a rally to the Alsace I am organising, it offer great value. Both sites mentioned are in ACSI if you are a member and going out of peak season.
Have a great time it is a beautiful area to visit.