People who are suggesting to move messi into midfield position or in position behind a natural 9 should think twice before saying it. I mean it is too early for messi to play that role i can see him play in that position in future but not yet. He is still 26, i would wait until he reaches 30 to play him in CAM position.
Messi goal scoring talent is just too great to neglect and move from his usual false nine position. If he could play in CAM better pep would have done it with ibra playing front of him. But messi plays at his best in false nine position (most of the time). We only need him to shift to midfield or right wing when the opponents are parking the bus or 3/4 players marking him. He won't be able to do the awesome runs from midfield more often if he has a striker in front of him. He will have much lesser placce. He will still score many goals but it will be more tough for him to score from midfield. He will assist more though, but i don't think we should play a striker in front of him in every match. Messi finishing is one of the best in the world (IMO he is the best finisher). We already have cesc for giving assists, his vision for through balls which will become really important for barca in future is best in the world
False 9 is the perfect place for him to play and an occasional shift to right wing or playing behind a striker will improve barca against bus parking teams. That is why barca should try for an experienced striker rather than sure starter like aguero.
You are correct that moving Messi to a primary midfield role would be entirely too premature right now. He simply is too good a scorer to move him further away from the goal and to give him responsibilities that would make him less of a scoring threat.
However, that and getting him a striker help are two different things. Getting Messi a true striker will only enhance his current role. He would still move around between the CF spot, the wing, and the midfield like he does, but now the striker is occupying defenders, dragging marks, taking all the contact, and giving Messi a lot more space to operate, which just makes him all the more dangerous. The objective of the striker is to simply give Messi more freedom and space so that he can be his deadly self.
Neymar too for that matter, would benefit astronomically from a striker help. Both Messi and he would operate within the space afforded to them by the striker moving CBs and dragging marks with runs and movement.
Though, for this to be effective, IMHO the striker needs to be a world class striker. You cannot get second tier type because his threat level will not be enough to threaten defenders and force them to move when the striker does.