I'm apparently in the minority, but I agree with your decision.
Challenges to right-of-way purchase prices are routine - there's a whole cottage industry of lawyers who specialize in representing property owners. I believe in the old law books there is something about eminent domain, fair compensation, and redress of grievances.
I've never heard of the EIS procedures being dragged into the determination of land value, however. (Limited knowledge - I mostly work on locally-funded projects, and we don't follow the full NEPA process used in federal-aid projects.)
Of course, in the old environment when property values "always" rose from year to year, an appraisal performed at the time of an offer could be presumed to be at a higher value than one pulled together using last year's sales comps. Sounds like a sharp lawyer is trying to make a case that fair compensation is the land's value at the time your agency was "ready and willing" to buy the land, as measured by some 2007 milestone in the EIS process.
Engineers don't get called to the stand to talk about land values. From what you have posted, it appears to me the DAG is just doing due diligence to put together a definitive EIS timeline for use in case the plaintiff and his land value "experts" make some progress on this theory with the court.
On compensation, I think $100/ hour plus travel expenses is a very fair rate for a consulting engineer with your experience. Bumping it up to $150 or $200 in the event court testimony is required would not be unusual.