Hi Nige  ( nice banjo...)
intersting questions that can't really be answered truthfully.Each Village/Town/area will have it's own rules and regulations so there is no general rule of thumb.You are always better to bu a ruin,at least that way you have a pretty good chance of refurbishing or rebuilding without to much trouble.
Land on it's own is different,the local ajuntaments in each village are clamping down as they see the brits coming over and building whatever wherever without P/P although these rules are set in concrete they do bend........a quote from a local architect.Building an Almecan is a way around this but you will need to speak to the architect.
Secondly,not to sure about the prices quoted /m2 sounds a bit excessive to me,even for the costas,but I will stand corrected,I've certainly been quoted cheaper.
Lastly,if you're looking for land or property give this guy a call  www.bonaterraproperties.com  .He has some good land and properties,his name is Franc,he's local,he's Catalan,he speaks pretty good english and he DOES know all the right people and he's a good laugh and NO I'm not on commision but mention Ian and Steph,it'll be worth a drink to me......He will probably take his time replying but keep trying....
Ian