I think they finish this year with Manny, and they should. In the last few days we've seen how much of an impact having the Dominican Duo can have on the offense, and this is without them both going bonkers with the long ball, which can and will happen. Manny is auditioning for a new contract right now. He knows his option isn't getting picked up, and he knows there are questions about his professionalism at this point. I think the chances he pulls something immature and tanks on his team are slim. He's got his last big contract, one that he wants (why else would he be so upset about the options), to consider.
For next year, it may be worth it to give Brandon Moss a look as an everyday outfielder. He's hit well in his time with the big club this year with limited regular playing time. He's looking like he has legit 25 HR power, and he'll play much better defense in LF (or RF with Drew upgrading LF). The downside is he will make the middle of the order very LH, but with some creative lineup construction and Youk coming into his own in terms of power, they may be able to mix it up some.
Try that to start the year. If it's not working out, look to pick up Holliday at the deadline, because Colorado will be looking to maximize return as he approaches his FA offseason.
That, or beat the Yankee offer to sign Dunn.