IMO getting a striker for starting 11 is a terrible idea, only would go for it if all our wingers suck badly(which is currently not the case). Experienced striker as plan B is very good i think, still would not jump into conclusions until feb and mar next year. Let's wait for big matches to come and then think about we need a no. 9 or not and let messi come into full fitness also.
Tata is still experimenting and may be we don't need a new no.9, may be could use neymar or sanchez as a strikers. Already neymar and cesc are eating up messi space on field, obviously would not want another hot head striker to limit messi. Messi is played at right wing only because he will be marked less not because he will run on wings( he don't have the pace he used to have four years back) and put crosses and passes to some stupid striker. Messi behind a striker may work in argentina but not in barcelona, argentina have average midfield but we have one of the best in the world. Where will messi play behind a striker in barcelona in cesc/xavi/iniesta place???.
If we buy one striker next year( which is presently not needed which may change if sanchez flops again) he should be quick, tall, strong and should be able get behind parked buses. I would like aguero but can't see man city selling them anyway.