My doctor also wanted me to go on imuran after my surgery. I did not agree as I was symptom free and imuran does not guarentee anything. He did suggest I quit smoking (which I am on again off again) and said that it is probably just a matter of time before it comes back. He did like the fact that I work out 3 times a week and kayak on weekends. (said it was probably keeping me in remission). Anyway it's been 3 years since my surgery and I feel great.
If the crohns does come back I will re-think the imuran but in the mean time I do not see the point of inviting a host of other problems to try and combat something that may or may not come back.
Do what's right for you. Weigh the pro's and con's and maybe look into other aspects of your life to help keep you in remission. Good luck.