[hotpockets]

First make sure your enthusiasm for an idea is not resulting from hidden assumptions you have made and not realized. Examine all your assumptions.

Also try to avoid falling prey to any cognitive biases. There is a list of them at wikipedia that is probably worth acquainting yourself with. Perhaps you might favor one idea over an other just because you have been thinking about it more recently. This would be related to the Recency Effect - increased saliance and recall of recent stimuli. Thus you will weight the benefits (and drawbacks) of recent ideas more than the benefits (or drawbacks) of past ideas.

One way around this might be to rate your ideas at multiple times after rethinking various past ideas fully.

http://en.wikipedia.org/wiki/Recency_effect