I wonder could those with any experience offer advice on the following.
Many people say if a basic song sounds or "feels" good it will make it without changes. Is this really true?

From my experience here at JPF in the 6 mths since I joined I have listened to some excellent offerings, containing tasteful and technically perfect musical parts played by session (as well as songwriting) musicians, and questioned if the song itself could be recognised as something good if it did not have all the professional 'input' (ie Rhythm, Bass lines, licks etc).
So my question is;
From a practical music industry point of view, to what extent is the success of basic 'worthwhile' song ideas dependent upon the contribution of session recording musicians lifting the song to a special level with their skilful playing abilities and how common is it that an average or below average song is recognised as worthwhile going with (or even a hit)?

I understand musicianship on any recording is important and would guess that industry professionals can be successful if they possess an inate ability to recognise if a particular song, that we consider to be so-so, could be a hit with the changes they wish to make on behalf of the writer who after all may accept changes if it means it gets mass produced on a CD.

In case you are wondering. Although I am doing all this out of pure enjoyment/enthusiasm right now, any advice would be for future reference when I may select some of my songs or basic song ideas for the 'studio session' investment to (possibly) increase the chances of commercial success.
Tony