I agree that Crouch, Pav and Defoe have all been left wanting in front of goal this season. But if we are talking about moving forwards next year then we definitely need to make some changes. Personally I think Pav is our weak link, although he has scored more than the other two. I think we should keep hold of crouch, because although he does not always score many he does create a problem for the opposition and is completely different to most other strikers. Pav would be better suited at a team like Everton, who work hard and need a player like him, I think he would score some goals for them, but he is not Champions league quality.
As for Defoe, he has been extremely poor this season and there is nothing worse than someone playing badly and then spitting their dummy out and blaming others for their own incompetencies. That being said I think he could still be effective for us, as long as he swallows his pride and starts putting more effort in to proving everyone wrong and demanding a place in the side due to his quality rather than his ability to strop!
If we are only able to sign 1 player then I agree it needs to be someone young, strong and deadly in front of goal and it should be Pav that makes way. If we decide to lose Defoe as well then they could be young, quick and small and the other could definitely be someone like Drogba, he is not too old, would having something to prove and if anyone could extend his playing career at the highest level it would be Harry.