I think the recall would be done regardless of mileage. As far as the upgrade to the ECU/TCU and revised accelerator pedal - those are part of a TSB (Technical Service Bulletin) that aren't really supposed to be done outside of the warranty period - not saying you won't find a dealership that might do it, but they don't have to.
The warranty will depend on the mileage and if any extended warranty was purchased. Unfortunately I don't know what the standard warranty was. The $2+$3K sounds about right to keep in as-new condition assuming everything is up to date for the most part. My guess is that nothing much has been done so far - so the best you can hope for is the TSB updates, and good fluid maintence.
Oh, and you might check
http://www.infinitihelp.com for some of the TSBs and recalls that apply.
I think we'll know a lot more after you get a copy of the service records.
Heath