>I have a perception that a full frame camera will give me a >"spot-on" sharper picture - (if I am willing to >upgrade the lenses of course.) Am I wrong about that?
Basically, yes - as a general principle you are wrong about that
How FX stacks up against DX all depends on the camera(s) being compared. I shot with a D300 (12MP, DX) and a D700 (12MP, FX) alongside each other for a year or two. The D700 led in low-light performance, because its images were cleaner at high ISO settings, but in sharpness, colour and contrast there was nothing to choose between them.
If the results from your 50mm lens don't meet your standards for "sharpness", I don't think a new camera (of either format) will improve things much.