As far as I understand from Bhagavad-gita, Krishna-centered karma (nishkarma-karma) is a wonderful thing because it purifies the heart and makes one eligible to gradually come to the platform of nirguna bhakti-yoga, pure devotional service. There is no other way to purify the heart from those inclinations for karma. The process of Bhakti deals with anarthas and stuff, but if I have inclinations for karma I should go through the cycle: sakama-karma - nishkarma-karma - nirguna-bhakti... that is: 1st I can't entirely work for Krishna's pleasure (too many selfish material desires), but being a religious man I dedicate some portion of the results I obtain from my actions to Krishna (like donations and stuff) - that is sakama-karma. Then after some purification and by the mercy of Guru-Gauranga I get the inspiration to dedicate my professional work fully to Krishna and His devotees. By the time I possess a strong faith that my material needs and expectations will all be perfectly met automatically, so I don't even have to worry about it. Then on the strength of such an inspiration I work tirelessly day and night for Krishna. However, I still have the inclination for the type of proffessional work itself I just do it all for Krishna. That is nishkama-karma, in my understanding. Please correct me if I am wrong..
Then as a result of this purifying work and by more mercy of Guru-Gauranga I gradually come to the platform of complete absorbtion directly into the activities of bhakti with a clear vision of my goal in bhakti, off course. That is nirguna-bhakti-yoga.
All stages seem to be very important, as they are linked one to the other, and are all pure mercy of Krishna. Otherwise, Krishna would probablynot waist His time speaking the 3d chapter of Bhagavad-gita.
Please correct me if I missinterpeted something. I wrote this down just to refresh this in my brain.