Wadler's work is great, I've seen his talk on this many times (where he has the lambda shirt on), but it doesn't really cover "why it is useful" just "why it is inevitable".
Really, how would you scientifically show that parametric polymorphism is "useful?" "Useful" isn't a very empirical property, it isn't something you can reliably measure. In a scientific paper, you can't just say something like:
> When it comes to maintaining and evolving these systems, the lack of explicit static typing becomes a bottleneck.
without justification! You have a citation, or perhaps it is something just accepted universally (which it isn't, of course). At the very least, you have to weaken the statement a bit...like:
> When it comes to maintaining and evolving these systems, the lack of explicit static typing is probably a bottleneck.
You can't talk in absolutes without evidence. But you know, the benefits of static typing are clear via anecdotal experience, we only really argue about whether or not the benefits balance out the disadvantages of static typing (and how those disadvantages can be mitigated, and if that is enough...). Again, in arguing about this we are firmly in the area of design and not science.