I´ve bought both off-plan and resale in my time. Contrary to what you read from most people on this forum the off-plan was a much smoother experience for me. However, I didn´t buy on the Costa del Sol.
I think on the CDS at the moment the way forward is definitly resale – you can haggle prices down and illegal off-plan properties are rife there.
Where I chose to buy it is the other way around. Resales are very expensive compared to off-plan and there is no “buyers market” so the sellers will not be haggled down at all, and they won´t sell to you unless you agree to pay black money.
I think what I am trying to say is do your investigation into the area where you are buying – don´t be put off buying in Murcia just because a load of people bought from crap developers in the CDS. Their experiences may not be relevant to your experience (but on the other hand maybe Murcia is just as bad as the CDS? – I don´t know the area so can´t comment).