Hi,
I am not fully sure that I understand your questions but I think they are:
Q1) Can having a weak provisional (e.g. no figures, not enough detailed description, etc.), hurt your chances or limit you when it comes time to filing a non-provisional?
A1) The non-provisional does not have to be indentical to the provisional so even if you filed a weak provisional, this should not stop you from filing a better (more proper) non-provisional.
Q2) If the best mode and detailed description is expanded upon in the non-provisional, can you still rely on the provisional's early filing date?
A2) It depends. If you are trying to claim piece X in the non-provisional and piece X was shown and mentioned in the provisional than you can use the provisional date for claiming piece X. However, if you are trying to claim piece Y in the non-provisional and piece Y was not shown clearly shown or not mentioned in the provisional than you cannot use the provisional date for piece Y.