You'll get all the EV benefits without the depreciation hit of a new vehicle - nor that of any vehicle with a combustion engine (making the volt and prime poor choices because of the depreciation as gas engines go out of favor)! Depreciation needs to be factored when crunching the numbers of owning any vehicle.
I don't think it's accurate to predict depreciation for PHEVs because they aren't EVs. I think it's more likely that they will depreciate less, for two reasons:
* No substantial loss of driving range over years.
* As more drivers with long commutes and some range anxiety consider alternatives, the PHEV will continue to be their safer choice.