If your primer is covering up the detail you are either spraying it on too heavily or are using a primer that is not designed for models and is just too thick. I also prefer Tamiya Fine Surface Primer, and it works quite well.
You don't always have to prime prioe to painting. Priming serves two basic purposes:
o It provides a solid color coat for the subsequent paints. This is important if you have done a lot of putty work as it makes everything the same color prior to the main color coats. It also makes seams in the joints easier to spot.
o It allows the subsequent paint to adhere better. Primers are designed to adhere to abre plastic very well, and other paints typically adhere to the primer better than they do to bare plastic.
When painting with enamel or laquer a primer is not an absolute must since both of those paint types adhere quite well to styrene. If you are using acrylics then I feel that a good coat of primer is very good insurance against paint pulling up when it is masked, and other problems associated with acrylic adhesion.