Use High Priority Site as Innovation

Nope. Just cite the credit from the Innovation Catalog, provide the little narrative needed, and upload a copy of the map showing your project location in one of the qualifying areas. I've used this several times on various v2009 projects with no issues.

Is the same true for ID+C projects LEED V4? Is this credit applicable? While I found this credit to be applicable for ID+C, the credit language is confusing. Below an extract from the USGBC website. 

RequirementsOption 1. Historic district (1 point BD&C except Core and Shell, 2 points Core and Shell)Locate the project on an infill location in a historic district.OROption 2. Priority designation (1 point BD&C except Core and Shell, 2 points Core and Shell)Locate the project on one of the following:  ...

As long as the strategy shows up under ID+C v4 (or 4.1) in the Innovation catalogue, you are fine to use it. All Innovation strategies are only worth 1 point, except for a very few specific exceptions. Only one that immediately comes to mind is the O&M Strategies one where you can get 2 points as explicitly explained in the language of that listing. Sometimes for Innovation, if it's pulled straight from the language of the original system, you might have requirements or info listed that just don't apply to ID+C project types.I've used this strategy on ID+C v4 projects, too, with no issues.