That is true, you can improve anything to your likes etc.
I have to ask you seriously just for the record.......if this was an ongoing project wouldn't you prefer to have the R8 spindle.....it opens up a whole world of possibilities.......I don't know if it's possible to just swap over the innards to get to R8.
I don't think "crashing the carbide into steel" is an actual happening......the wear factor for fast feed rates and higher speed is one thing you want.......I doubt that a hogging mode would be indulged with........CNC is all about many light cuts which for a manual application would drive you to drink.
Many light cuts and a fast feed rate maximises the ability of the machine to resist deflection due to a relatively light build.
Anyway, best of luck with the sale....hope you get your price.
Ian.