I had the same problem (sinky legs) but found if your head is in the right position your legs stay up more. I kick a lot less now and find swimming less stressful. My swim instructor told me that some of the best swimmers only get about 10% of their propulsion from their legs.
The better I swim the less I kick and I am getting faster. I do believe there is a balance, but often find if I swim in open water (in a wetsuit) I forget to kick all together.
Train yourself to kick your legs, that will give you stability and nice body position in the water, but do not give it all during the race. Just have a nice steady effortless kicking.