Ken Griffey Jr. Rookie Card: This is widely considered the most valuable card from the 1988 Score set. Griffey Jr. went on to have a Hall of Fame career and his rookie card remains one of the top rookie cards of all time. In near mint to mint condition (graded 8-10 on the 10 point scale), Griffey Jr.’s 1988 Score rookie will fetch thousands of dollars today. In a PSA 10 gem mint grade, it has sold for over $25,000. Even in lower graded condition (PSA 5-7), it still retains value in the hundreds to low thousands typically. The Griffey Jr. rookie is iconic from this set and remains the undisputed heavyweight champion in terms of value due to his legendary career and status as a fan favorite player.

Nolan Ryan record breaker card: This special medallion card commemorates Nolan Ryan breaking Sandy Koufax’s record for strikeouts. It features a piece of the actual ball Ryan used to break the record. Only 250,000 of these cards were produced, making it one of the scarcer cards in the set. In high grade (PSA 8-10), it can sell for $150-$500. Even in lower grades (PSA 5-7) it holds value of $50-$150 due to the low print run and the historic achievement it honors of Ryan. Any Nolan Ryan card featuring one of his many records broken throughout his career tends to be more valuable to collectors.

Ozzie Smith autograph card: This autographed card of Ozzie Smith is one of the rare signature cards found in the 1988 Score set. With Smith’s autograph officially authenticated and in high pristine condition, a PSA/DNA 10 gem mint grade would be worth $500-$1,000 today. Even in PSA 8-9 condition it still commands $150-$400. Getting a true Hall of Famer’s autographed card from their playing days is highly desirable, and Smith’s defensive wizardry and popularity adds extra cachet to his signature on a card. Condition is critical to its value given the scarcity.

Ken Phelps rookie card: Admittedly, Ken Phelps did not pan out as the star many thought he could become when he debuted in the majors in 1985. His rookie card still retains value due simply to being a legitimate rookie card from the set. In near mint to mint condition, it can sell in the $15-$30 range. Not nearly the value of stars like Griffey Jr., but as a true rookie issue it has its niche collectors. The key is high grade and centered registration to maximize its value potential within the set.

Mark McGwire card: Sure, McGwire’s home run chasing feats and records came later in the 1990s. But he was already establishing himself as a budding power hitter for the A’s by 1988. Any quality McGwire card from the late 80s retains value due to his iconic career and popularity as one of the game’s great sluggers. His 1988 Score card in high grade (PSA 8-10) can sell for $10-$25, and is a nice collection piece outside the headliner Griffey Jr. issues. Even in lower grades (PSA 5-7) it will usually sell in the $5-10 range. McGwire’s stature in the game carries value for his older cardboard.

Orel Hershiser card: As the National League’s Cy Young award winner and owner of a 59 consecutive scoreless innings record in 1988, Orel Hershiser’s achievement was as fresh in collector’s minds then as it is today when they opened Score packs. Any quality Hershiser card from this era commands attention. For his 1988 Score issue, a PSA 9-10 mint version can be worth $15-$30. Even lower graded copies around PSA 7 still carry an estimated $5-10 price point. With such a standout season so recently behind him in ’88, Hershiser’s cards offer historical significance mixed with on-field accomplishment.

Those would generally be considered the most valuable 1988 Score baseball cards to find in a collector’s collection today. Keys are high quality condition grades, whether autographed, rookie cards of future Hall of Famers, or special achievement cards of singular historic performances. While the Griffey Jr. rookie understandably leads the way, there isValues can vary up or down a few dollars based on current active auction market conditions. But those price ranges serve as decent guidelines for the premium cards to look for when collecting or investing in vintage late 1980s baseball memorabilia. Let me know if any part of this lengthy answer needs further explanation or expansion.