If you have the ability to create new fields you would want to create a separate demographic score - this way you are looking at interest and fit on two dimensions - you don't want to false indicate readiness just because they are a good fit.
Sales Insights also maps to two fields, we use master lead score for flames and demographic score for stars to show.
To show the full potential (not sure if you can do it in Spark) in our Enterprise edition we use Lead Score as our master lead score, we increment it with each lead activity. However, we have individual business unit lead scores to measure activity towards BU MQL. So for a given activity we increment BU score +XX and Lead score +XX but when the user goes to MQL we reduce the BU score back to zero and start again.
With additional activity the cycle continues. This allows us to see where they are with respect to each BU MQL and then the Lead Score becomes more of a lifetime value score - so we can also compare against other MQLs, who is fresh and who has considerable interactions with us.
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