If you ask most people what they're trying to accomplish in any fantasy baseball league or contest, the answer will that their goal is to do as well as possible. Sometimes that's a reasonable answer, but in some formats you're forced to choose among multiple goals. One obvious example of this is in the high stakes contests like NFBC or WCOFB. Is your primary focus to win the overall prizes or to ensure that you win your league? You can try to balance both goals, but by doing you make your chances of accomplishing either one worse.
How to treat the current situation with Jose Reyes is a perfect example of this choice. Let's say you're drafting in the NFBC this weekend. Jose Reyes is supposed to rest for the next "approximately 2-8 weeks". If his thyroid condition has improved at that point, he can start getting ready to play. In other words, he could conceivably be back by Opening Day...or we could learn in mid-May that he needs to miss more time. Let's assume that his current situation causes him to be drafted in the 4th round, instead of the 2nd round where he was going in most drafts unil the latest news broke.
So is Jose Reyes worth a 4th round pick right now? That completely depends on your goals. If you want to ensure that you win your league, I think he's too high a risk. This guy could miss half the season. On the other hand, if you want to beat out hundreds of other opponents for the top overall prize, you need to swing for the fences...and getting a first round quality player in the fourth round would be a great way to do that. If you don't think through your goals ahead of time, you may end up with a blended strategy that fails on both counts. You'll pick some risky players, some safe players, and end up with less than your share of league victories despite never putting yourself in position for a high overall finish.