John and Phil have made some good points in this discussion. An important one is that using a few Gestalt techniques isn't the same as doing Gestalt Therapy any more than using a cognitive technique or two is the same as doing Cognitive Therapy.
To master either approach, training and supervision would be really valuable. Certainly, an intelligent, tallented person can learn a lot from reading a good book and trying the ideas out in real life, but would you really expect that reading Interpretation of Dreams would transform the reader into a skilled psychoanalyst? Neither Gestalt Therapy nor Cognitive Therapy is so straightforward that a good text can convey the richness and intricacies of the approach
As far as the question of whether Cognitive theory is large enough and rich enough to provide a philosophy of life, I guess my answer is that while Cognitive theory hasn't tried to provide a philosophy of life, I don't experience my philosophy of life as being separate from my understanding of my clients and of therapy. Cognitive texts are fond of quoting thinkers such as Buddha and Epicetus as fore-runners, so I guess one could develop a decent philosophy of life from Cognitive Therapy if you wanted to.
If you want me to speculate more about Cognitive Therapy and the meaning of life, you can find me at the Cognitive Therapy forum.