Once a player hits free agency, you can not consider the investment made into their original draft position. It has no relation.
Drafting someone in the 1st round or top 10 picks or in the 3rd round has no bearing on the ability to re-sign them as a free agent. To suggest that their is a return on investment post rookie contract is to misunderstand what the initial investment was.
Put together an ROI formula and you'll see what I mean. Once you sign them to a new contract you are making an entirely new investment not based on the original.
You are talking DPROIFRC (Draft Position Return on Investment for Rookie Contract), you know it does not work that way in the NFL and that is not how FO's view their ROI for drafting a particular player.
FO's draft a player high because they believe they will be a part of their organization for a decade or more even after the first contract. Because it allows them to negotiate in ways other teams can not (value), control a player in ways other teams can not (value), gives them leverage that other teams do not have (value) and have more information about a player in ways that a team who does not draft that player can (value).
The ROI includes more then the rookie contract, if a team that drafts a player can negotiate/ control a player in a way that gets that player for less money on their next contract because they made the investment to draft that player in the first place. That is return on investment for drafting them in the first place, even if they are making another investment.
By drafting a player it gives you certain controls that are of value that can only be measured by the full life cycle of that player when determining ROI for a player relative to drafting them.