Chardonnay,
I have recently completed on my penthouse situated in the same Manzana. All the documentation from Penarroya is present and correct to complete with a mortgage and you will be accruing interest every day that you choose not to do so, as you agreed and signed for in your contract agreement when you paid your initial deposit in 2003.
I think that your view that you can now choose to sue for your deposit to be returned because you only intended it to be an investment is terribly misguided - under what reason can you sue? Okay, so the development is late, but it is now ready and the documentation supports sufficiently for completion with a mortgage - you choosing not to is not a valid reason to sue and to attempt to do so will cost you even more money without any return.
Also, beware! I sought advice from several solicitors and found ME to be helpful and efficient. A lot of solicitors will be happy to tell you what you want to hear so that you choose to sue and they can charge you literally thousands of euro's more for a brand new case which holds little strength. ME are far more realistic and impartial. I could have chosen to sue, but recognised that completion is possible and far more cost-effective in the long-run.
Finally, if you are not in a position to complete, Penarroya may be able to offer your apartment for re-sale in their office on the development. I'm not sure of their terms and conditions regarding this, but at least it is another option.
Best of luck.