Hello Irene,
My husband and I just spent the entire month of May in Colmar and have a completely different opinion than the other posts with regard to needing a car but I do understand their perspective. The train/bus systems are outstanding if you are willing to spend just a little bit of time to figure out where you want to go and how. Being able to sit back, enjoy the ride and watch the sites rather than worrying about parking and directions was invaluable. Parking in Colmar, in particular, is a pain. We used the train to travel to larger cities and were able to take the bus to some of the smaller towns. During our time there we utilized public transportation to take day trips throughout the Alsace, with ease: Strasbourg (train), Haut Koenigsbourgh (train and bus), Kaysergsberg (bus), Eguisheim (bus), Ribeauville (bus), Riquewihr (bus) and Turkheim (bus) and although not in the Alsace, we took day-trips via train to Zurich and Bern, Switzerland.
With regard to food- yes, it is very hard to find veggie or mostly veggie meals in Alsase. I am a healthy eater and was constantly on the search for non-meat options during our stay in Colmar. The best dinner we had by far, both for quality of service and food, was l'Arpege. They offer vegetarian and organic options. Also, our favorite place to eat luch was at the covered market- there is a restaurant stand there (with tables and chairs so you can dine in) named Legumes-Moi, run by the sweetest couple. They offer a differet vegetable soup every day, very nice salads and other vegetable options at a very reasonable price. They wil also do a fresh veggie or fruit juice, if you ask. We ate there so often that they sent us on our way with a nice jar of homemade preserves when I told them that it would be our last visit. Whether you are at Legumes-Moi or another restaurant, your best bet for ordering a salad is to order the "crudités" salad, as it is all veggies. Most "mixed" salads are served with meat. Beware, very few restaurants offer menus in English and very few servers understand Enlgish so make sure you are able to state your requirements in French (my #1 requirement was "sauce au par" for salad dressing on the side)!
Happy Travels!