Upgrading parts is interdependant.

Right now you have a very mild cam and the full boat TTI setup will probably not net a substantial difference, certainly not $2000 worth.

Putting in more cam will probably not see as great an improvement with manifolds as it would with headers.

But then again, if the intake system is the bottle neck you need to improve that as well.

Vicious circle.

And as you up the HP potential the cycle only becomes more pronounced. But any one of those changes will show some improvement and as you can afforded upgrading the other areas will enhance that improvement.