He will have an actual target in the front making good runs. Yes I know that for the past year he has been ignoring runs or is just not fast enough to release the pass like used to in previous seasons. But the more choices and chances he has, the better he'll look. He basically just needs more movement, or atleast cleverer movement. He's not getting that consistently anymore. Sanchez's off-the-ball runs were amazing in 12/13, not so much this season. And his movement is of the very obvious type.
Xavi should go to another club and profit like Pirlo.
You can just make the team play a bit more centrally and have the current players return to making more diagonal runs into space.
IMO the biggest effect a strike is going to have on Xavi, and the rest of the players and the team for that matter, is that a striker is going to unclog the middle of the field. Right now the middle of the field is too congested and there is little space to maneuver. With Xavi's loss of mobility, this makes it harder for him to be as impactful.
A striker would pin back and keep those CBs honest, and let the rest of the midfield have to tangle with both Messi and Iniesta, giving Xavi a lot more valuable space to operate. Opponents midfield would also not be able to go out onto the field too much because that then creates a big gap between the midfield and those pinned CBs keeping an eye on the striker, gap which could be really exploited.