Here is some info that may help answer your questions:
Will nursing affect the nutrition of my unborn child?
This concern is valid for malnourished mothers, but it does not appear to be grounded for well-nourished mothers. Although we do not yet have a medical study that can speak directly to the question for well-nourished mothers, we have two reasons to be quite encouraged:
A survey of 57 mothers who had breastfed during some or all of pregnancy recorded that the babies born to these mothers had healthy birth weights (birth weights averaged 7 lb 9 oz, and ranged from 5 lb 9 oz – 10 lbs 14 oz). (Moscone 1993)
A recent review of the available research on breastfeeding and pregnancy as separate events revealed that as long as the mother is eating enough calories of a basic mixed diet, and as long as she is gaining weight within healthy parameters, there is ample reason to believe she can provide well for herself, her fetus and her nursling. (Adventures in Tandem Nursing, 2003)
The changes that accompany the decrease in milk supply would be expected to affect the taste of the milk, and indeed some nursing toddlers mention the change in taste to mom. Once the milk is mostly/fully colostrum, the taste may change again. Some nurslings don't like the taste change (particularly when combined with the concurrent reduction in milk supply) and may wean as a result. Some love it. Others either don't seem to notice the change, continue nursing despite the change, or simply don't mind.
There are tons of Q and A stuff on this site about that subject:
kellymom.com :: Nursing During Pregnancy & Tandem Nursing