SANTA MONICA, Calif., April 6, 2000 - The over-scrutinized sexuality of Academy Award-winning star Kevin Spacey has been over-scrutinized. Again. In the April 11 issue of the Star, the tabloid-par-excellence goes full tilt with a centerfold report featuring one salacious headline ("Revealed! Oscar winner Kevin's mountaintop tryst with young male model") 12 pics, and several groaner captions (including "Male Bonding," "Gay Old Time," "Out and About" and - yeesh - "Going Down"). The report all but says the sexual preference of the actor is really of the same-sex variety, despite what he insistently professes -- i.e., that he's strictly hetero. So, has tabloid journalism sunk to an unprecedented low? "Well, I actually think it's a slightly more problematic issue," says Jeannette Walls, MSNBC gossip columnist and author of the just-published "Dish: The Inside Story on the Wo