I agree with your sentiments completely.

If I want to give up a guy like Tim Salmon for the first or second (or even third) pick in a Monthly that may or may not net Kerry Wood, or Barry Zito, or Matt Morris, etc then I should have that right. Likewise if I hold the pick I should have the right to trade it for an alternate player.

My impression is that the reason they don't allow trading those picks is due to lack of administrative resources. I am with you and would like to see a policy change in this area (if feasible).