We had the same debate however initially finances dictated that the air con be on hold.
We've now spent two summers out in condado without Aircon and managed with £5 fans in each room (bought from Woolies just before their demise). We have got the benefit of louvered shutters on the front paio doors so were able to shut them and leave the patio doors open to allow some airflow.
We've managed without and although a litttle uncomfortable on a couple of evenings this year I still can't quite justify the expense of full Aircon and running costs. If we were there for the full 6 weeks of summer or were there in mid winter when heating is required then may be the cost would be justified.
Also - if I were renting I think it is a must as the number of apartments being rented on CdA if one apartment has it and the other doesn't I know which one I would choose to rent!
For now we are happy to go without and may also go the ceiling fan route to replace the upright floor standing ones we have (much quieter at night).