We've always thought the Chevy Lumina would be the perfect illustration for the generic "car" entry in an encyclopedia. The Lumina has all of the basics and none of the frills. It is sturdy, reliable, roomy, and inexpensive. It scores at the top of the charts in crashworthiness and at the bottom in theft rates. With traits like those, you won't be surprised to learn that the Lumina gets little respect from car buffs. Neither will you be surprised to learn that the Lumina was among the top-10 cars in sales last year. A solid car at a solid price will always have a market. For 1998, the Lumina continues in its honest ways, although it has picked up a few frills. OnStar, GM's nifty navigation, security and personal service system, can be added as an option. And the performance-oriented LTZ model, which debuted last year, has a better, more reliable powertrain package this year.