It is a tough question, but I guess in general you always draft as if it's a keeper because you just never know what will happen to that 'solid core'.
It also depends on who's available. If say you keep 5 and Rickie Weeks is available, you take him first round. Even if that means over someone who may just outprodue him this year (like a Kent).
There are some amazing prospects on the horizon. Delmon, Butler, Upton, Drew