Question concerning the VWP, Visa Application denial and ESTA

Hello there, friends. I have a bit of a detailed question. I am a Spanish citizen who has been living in Spain for the past 3 years. During these years I have traveled to the US on the VWP on 2 occasions, each time returning to my country within the allotted time period. Recently I applied for a Tourist Visa (Non-Immigrant Visa?) because I wanted to stay in the US for more than 90 days to visit with some good friends of mine. My application was denied because I was deemed to not have sufficient job security. I still have my approved ESTA from the last time I traveled and it is supposedly valid for 2 more years until 2011, so I don't know if I should apply for an ESTA again and risk having the authorization denied because I was recently denied my visa, or if the customs officers won't have an issue with me using my old ESTA. Basically my question is, should I travel under the VWP with my old ESTA? Does the fact that I was denied a visa recently mean that I have a higher risk of being turned away while traveling on the WVP, despite all my past entries? And, how much money exactly do customs officers consider sufficient funds to support onself for a 90-day stay if I am staying at a friend's house? I just want to do all I can to increase my chances of getting in, as this trip is quite important to me.

They want to make sure you are not basically moving here over time and too many VW visits results in them inquiring more.

You should consider some longer term visas if you want to be in the US that long and that often.

By the way Europe does the same for US citizens that hang out in Europe too long...