Joe,
If you want to try some top dressing ballast this spring give this a try. Go to your local feed store and ask for Red Cross Pigeon Grit. It has a better consistency and color than oyster shell chicken grit. Buy a bag or two to test with. Sprinkle some between and along the sides of a section of track and rub it level with your fingers. If you like the look then go for it. If you do go this route I recommend you finish it off with a watered down glue mixture to keep it from splashing out with a heavy rain. I use a 50-50 mix of water and Flexbond II that you can buy in gallon jugs. To help with spreading ballast what I did was fashion a spreader cup from a 10" piece of 4" diameter PVC pipe. Stand the pipe centered across a section of track, mark where the rails sit against the edge of the pipe then cut slots so the pipe will set down to the top of rails. Fill the pipe with ballast and spread away, finishing up with your finger tips our an old paint brush, use a spray bottle with water to lightly water the ballast and get the dust off the ties, then apply the glue mixture.
Ron