As long as large states like California, New York and Texas do not change from a winner take all system, it is not in the interest of small states like Colorado to do so.
I also don't want to forgot to mention that it also violates the federal election code. The method by which the electors is selected must be in place before (as I recall at least six days prior to) the date the electors are chosen which is election day. Even if the a referendum were a valid mechanism of determining the method of allocating electors, this referendum is too late to affect the 2004 election. This referendum should be fought in court and removed from the ballot.
Article II.Section 1
The executive Power shall be vested in a President of the United States of America. He shall hold his Office during the Term of four Years, and, together with the Vice-President chosen for the same Term, be elected, as follows: Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.