I don't think that the dandelions add much for flavor. I've only done one batch but it turned out wonderfully and I'm planning on doing a much larger batch this year. Although the contribution of flavor may be minimal, they do, as you mentioned, add color. They also contribute greatly to the bouquet. I can definitley smell dandelions in the wine. The recipe I used called for lemon juice rather than acid blend and I also threw in the lemon zest from one lemon even though the recipe did not call for it. Golden raisins added body. I think the "citrusy" flavor it has is more from the lemon juice and zest than anything else. I'm sure the raisins contribute to the flavor as well.
As far as collecting enough I have the advantage of 2 small girls aged 3 and 5 who just love to pick flowers. I hand them each a 5 quart ice cream pail and tell them to have at it. They bring me the flowers and go out for more while I snip the petals off with a small sharp scissors.
Believe it or not a dandelion isn't a weed, it's a lettuce. They are not indiginous to the United States. A long time ago, someone, somewhere, must have brought the seed over here to grow some lettuce in their garden and let them seed out on their own. The rest is history. If you pick the leaves before the plant sets a flower they are actually quite good. They can be usedin salads but they get more and more bitter as the plant matures. They are also excellent if chopped and fried in olive oiland added to soups the same way you would add the leaves of celery. I do this with my Smoked Salmon Chowder.