The question hasn't been answered for last 48 hrs since the question is not framed properly and relevant data/sample files are not provided for ease of understanding your question.Please do provide as much info as possible so that the community can answer your queries as soon as possible.
Since we do not have data available, I have explained the solution from what I have understood from the question.
It seems, you just need how to place your dimensions and measures to create spark lines. This is pretty simple.
Look at this example
In the above image consider Category and Sub-category are dimensions similar to your Client and KPI, Sales is similar to your impact metric and Month(Order Date) in column can be replaced by any other date field.
Any sparkline chart can be built in a similar way.
Hope this helps.
Please follow up in case of any more questions right here or through twitter @gvsjkrishna
unfortunately I don't have the actual data we will be using for this yet. I have simply created a small set of "dummy" data just to use for experimental purposes. In any case, I have attached a packaged workbook alongside the wireframes of how I would like it to look for your reference. Please let me know what you think. Thank you again for all your help!
Also, I may have already mentioned this, but ideally I would like to put these sparklines in the same table as the other data items indicated in the wireframes such as client, date, KPI, comment, etc.
Let me know if you think this is possible!
I do not have the right version of Tableau to view your workbook but from what I could understand, I have provided the image in the above post.
So, the image shows that the sparklines can be shown on the same page along side different variables. But, as I see your wireframes, they cannot be directly replicated. Tableau has multiple workarounds in terms of simulating these views.
There is an excellent resource on converting excel like tables to tableau in this link - http://community.tableausoftware.com/message/171852 and Tableau Public
Hope this helps