The three million dollar research grant that you mentioned has something of a questionable premise when it says that the goal is to "explore ways to recycle and reuse that cosmic debris to create a sustainable in-space manufacturing (ISM) industry." While this sounds great on the surface, there would likely be a problem with the idea of developing the ability to reuse old space hardware as a way to "create a sustainable in-space manufacturing (ISM) industry".
Since their premise in my opinion is not valid, for reasons which I will explain below, this means that the complexity and cost of safely keeping ISS in orbit until then is likely not going to be worth it, especially if it would cost more to preserve it then to deorbit it. If this is the case then the answer to the question whether ISS should be preserved for use as raw material for ISM instead of being deorbited would be no.
The problem with their approach is that it would rely on existing and future space debris as one of the main sources of material, combined as they said with ISRU materials mined from the Moon. The first problem is that space debris is scattered all over the place in different orbits and would be difficult to collect together in a central location for processing. It's certainly not impossible, but that's only the beginning of the challenges. The next one being that once collected it's going to be difficult, labor intensive, and potentially risky to safely disassemble the old satellites, rocket stages etc. and separate them into the various needed materials. This would be difficult and somewhat risky if done by astronauts during EVA. In theory the pieces could be brought into a pressurized "hangar" where astronauts could work on disassembling it, although in some cases there would be concerns about toxic fluids and gases.
Robots of course could be used for some parts of the process, like moving pieces from one location to another. However due to the wide variety in space hardware design, the actual disassembly and sorting of materials will likely require direct hands on human involvement for the foreseeable future. Especially since other than exceptions like ISS and Hubble, most space hardware was not designed to be disassembled in space.
A big problem could be that the quality and quantity of materials that are obtained from space debris may not be a good match with what is needed for a particular manufacturing process. Especially considering that at least current 3D printing technology for example is very specific in its materials requirements.
And then there is the legal aspect of the approach, since pretty much all space "junk" is owned by someone. So each party will have to be negotiated with independently. Many if not most countries and organizations may not be too keen on having someone getting an intimate look at their hardware, even if it is older. This legal issue is already a potential problem even for deorbiting programs being considered that would go around and send old debris into controlled Earth reentry.
And finally there is the inescapable fact that recycling old hardware is likely going to be a very costly prospect, and this has to be compared with the cost of launching the same materials from Earth, which was one of your questions. This of course can only be estimated, but I think @ChristopherJamesHuff explained the problem pretty clearly in a comment which I have slightly paraphrased:
You also have to consider what it would cost to just launch exactly the materials you need to exactly the orbit you'd need. It's likely to actually involve less launched mass than the tugs and refueling launches needed to move (debris) somewhere, then move the recycled materials to where you need them, even ignoring the cost of the orbital processing equipment needed to scrap the decommissioned (hardware) and turn its materials into something useful.
In the end the first in-space manufacturing industries will likely rely on a combination of ISRU resources and materials launched from Earth, where the exact type and quantity of material can be controlled. While there will eventually probably be a place for the recycling of existing space hardware, that is very far down the road in my opinion, making it too expensive and potentially risky to other satellites and spacecraft to preserve ISS just for the chance that its raw materials might be useful one day.