One problem with MMP is that those who oppose party politics or too much official recognition of a political party would refuse to vote for a party, thus giving them half the votes of those who can vote for both. STV would be a preferable system from the standpoint of a FPTP supporter since it doesn't have to recognize any party.

Looking at it that way we could draw the following spectiom:

FPTP -> STV -> what I'd proposed above -> MMP -> pure RP.

 The main advantage that I could see with what I'd proposed above is that it's fair to both sides. unlike the MMP and pure RP systems, it doesn't force anyone to vote for any party without losing votes, but unlike the FRTP and STV systems, it does allow one to vote for a party if he wants to.

The weakness with what I've proposed above, at least in the crude form it stand in now, is that it would also be the most inefficient of the systems above, in that it would likely take a few days for the parties to decide how to strategically place their votes to get the maximum number of candidates.