This is a good question. I'm not sure anyone knows the right answer but I can tell you how I would think about it. First, for the allocations, it depends a bit how respondents are using your five point scale - if respondents tend to be all over the place, giving lots of 1s, 2s, 3s, 4s, and 5s, then they really are using their allocations as independent choices and that might incline me to think that the task weight should be a bit closer to 5 than to 1 (at least as far as considering the allocation questions goes). But if respondents do what is much more common, and provide strongly skewed answers to the rating scale, then some answers (definitely will buy, probably will buy) are appearing a lot more than others and and your respondents may not be using the rating scale as much more than a dichotomy - which would incline me to weight the tasks much less. Bottom line, I think your compromise of a task weight of 2 is a good idea, but I might also run it with a weight of 1 and a weight of 3 just to make myself comfortable that my results aren't too sensitive to my chose of one task weight over another.