I guess this excerpt from Wikipedia explains all of the hype back then, but the last sentence pretty much explains why not to "invest" in these hyped up rookies. Kinda like that Strasburg guy that's already been on the DL twice.
When Eric Davis first appeared in 1984, his physical talents gave him the potential to be one of the most exciting players in the game. He was a rare five-tool player with home run power as well as sheer speed on the basepaths. He made a habit of robbing home runs and elicited comparisons to Willie Mays.
Unfortunately, he was also highly injury-prone, never playing more than 135 games in any season.