Sure there is. Sometimes players reach these milestones just by hanging around long enough to reach them. Rickey Henderson had more than 3,000 hits in his career, and yet his lifetime batting average (.279) was surprisingly low for a guy who is supposed to be one of the all-time greats. Pete Rose is the all-time leader in hits, yet his career average (.303) isn't even among the top 100.
The 500-HR milestone isn't as common as the 3,000-hit mark, but as the "steroid age" of baseball progresses we're going to start seeing a lot of better-than-average (as opposed to "exceptional") players approaching this mark.
When I think of a modern hall-of-famer with relatively mediocre stats, I think of Yaz. But Yaz played in Boston and got a lot of PR that Palmeiro never got.
I agree with you about this, but Yaz had an odd career for a number of reasons. For one thing, he had the misfortune of putting up "good" numbers (by today's standards) at a time when pitching was more dominant than it is today. For example, he won a batting title in 1968 with a .301 average -- a figure that must be an all-time record for the lowest batting average ever to win a title.
He also hung around for way too long. If he had retired after 15 years instead of lingering for another 8 seasons, his "pure performance" statistics (career batting average, for example) would have been much better even though his "performance/longevity" statistics would not have been as impressive.