I am very supportive of a womans right to choose and respect anyones choice but I personally couldnt do it. I feel I would always look at other children and imagine what my baby would have looked like, what milestones etc. I have know several friends who had abortions at different times and several friends give birth to unplanned pregnancies (2 of them on their own with no father on the scene)
The only thing I can tell you is none of the friends who went ahead with the pregnancy regret the choice. A couple regret the abortion...(although 3 of them feel it was the right decision and have no second thoughts regarding it.)
Personally I think if it were the right choice then your hearts and brains will be 100% but then again I am certainly not in your situation.
My only advice would be as pp suggested - focus on the reasons you dont want another baby/pregnancy and see if you can sort through them - if you come to a stalemate then I guess that will be your answer.