It really depends on how your body works and operates. I have very large and muscular calves and thigh muscles but I am also very muscular all over and can add muscle (and bulk) fairly easily. I have a friend, who rides much more than I but is tall and slender and for the life of her can't add muscle. She is now hired a trainer and is seriously weight lifting in order to add muscle.
Actually adding muscle is a good thing - it will make you a better or stronger cyclist. What you are worried about is "bulk". It prevent bulk, keep spinning, using lower gears, make sure to ride aerobically not anerobically (ie spin not mash).
To me nothing looks better than a toned, muscular pair of cyclist's legs - on both men and women!