Re: Bottle vs. sippy cup
My son transitioned to a sippy cup sometime around 8-9 months (just up and quit bottles on his own accord). There wasn't any more waste or mess with sippy cups than there was with bottles for us. Unless you have leaky sippy cups, I don't think that much milk would get wasted. My son started using a regular cup shortly after a year (which was a lot messier, but we started with just water).
I don't see any reason to continue using bottles if they are not necessary, but I don't think there is any harm in it either. Ultimately, I doubt it makes much difference. I was happy to get rid of the bottles, personally.
K. Sophia - Mama to my little lactivore, the amazing Mr. X (11/10).