This is a great question, when to stop taking psychiatric meds.
What's important to ask yourself is; Why should I stop taking them? What is the cost vs. the benefit of discontinuing the medication?
In evaluating the cost, if you stop taking the meds; you fear being at risk for deep deep depression. The cost of being depressed may effect your long term goals, interpersonal relationships and overall state of well being.
Now analyze the benefits; From what you described, the only reason that you feel you need to stop is the inconsistency in your moods. In your ambivilance to taking Wellbutrin, if you talked about feelings of deeper depression or suicidal ideation, the benefit of discontinuing the Wellbutrin (safely) is that you'll rid your suicidal thoughts and open the door for other treatments that will not increase your depression.
Rewinding back to ambivilance, there's a normal period of time (in your case, 6 months) where one has to adjust to new ways of living. In my opinion, feeling indifferent is just being normal, which in essence, means that the MEDS ARE WORKING. Before you were use to living with depression and now you are experiencing a different way of thinking, where there are normal feelings, no depression or decreased depression. It's natural to feel confused and question the meds. It's an adjustment period for your brain in learning how to react to new feelings. If you're having a hard time adjusting, I would recommend that you work on this with a therapist. I've experienced a similar adjustment period and learned coping skills for adjusting to my new way of thinking.
If you're having trouble analyzing the cost vs. benefit, talk to people close to you whove known you before and after this 6 month period and see if they notice any difference. Write it down, discuss it with your Dr and your family and make an informed decision.
If you do decide to discontinue the meds, make sure that you do it in a controlled manner. Wellbutrin is a great antidepressant, but discontinuing it is very complicated and can result in some harsh withdrawal syndrome. You're Dr will be able to taper you off safely, but you must be monitored and 100% compliant with his/her instructions.
I've been on the med meri-go-round and I respect what medicine can and can't do, I enjoy living a happy life while on the meds and have no issue if I take them forever. Be smart about it and take good care of yourself in the process.