It will depend on the entry price for the new version (if there is one, if it's not at Detroit, it ain't happenin'). If as speculated it is 450K+, then the impact on existing GTs will be minimal. If it is 200K then ours will be impacted. So what? If it is a delivery miles car in a private museum you don't care, if it is driven you never expected it to go up and like a stock, value is only derived on sale.
I'm predicting, if the volume rumors are true, that the new vehicle will have production numbers in the 300-400 per year range, that it will be the former. Note GTE class homologation rules are:
Large vehicle manufacturer, 1 per week (52 per year)
Small vehicle manufacturer (total volume <2000 per year), 1 per month (12 per year)
To be eligible to race, large manufacturers have to produce 100 vehicles and small manufactures 25 vehicles.
So I expect Ford to be in the large vehicle class. Since a GTE car has to be "publicly available" to be driven, and since NHTSA and EPA certification is a multi year process, I will say again that they are behind for a 2016 introduction. But we'll see.