on my d300s, i'd say its about 99.9% acccurate, only 0.1% would be operator error, i.e. when i focus on my son running towards me, if i dont pan fast enough, camera will capture regardless of subject in focus,for portraits, im using a dynamic 21 point AFsetting without AF tracking on, for non moving subject its 100% accurate, i use this setting for a faster AF speed

When i switch to sports mode, -full 3D matrix, 51 points AF continous focuing, its dead accurate if it locks in a moving subject.

yes, rumours are that there will be a replacement by this year, maybe april like the D3200, maybe sept with the D7100, who knows......
if you can wait why not, but if you are passionate about photograp, then getting one now and go thru all the options and settings available would be a very interesting journey. E.g. my WB now i use K values based on the lighting available, most use grey card, i use my own instinct and judgement, the results can be very interesting at times