Engine upgrades vs originality- affect on value

I have a question regarding internal engine modifications and its' affect on car values. I was watching the German restoration video in this thread.

They brought the engine and transmission to Ruf to have it overhauled. They were discussing some performance enhancements but the mechanic there said that because this was a numbers matching car, that the engine should remain stock.

Do you think there were some off camera discussions about the budget and thus they decided to stay stock, or would unseen modifications really affect the value? I can't imagine anyone buying a restored T and devaluing it because it had been upgraded to a higher E or S spec. It's not like they were boring out the case for bigger cylinders.

Thoughts, opinions?

The presenter argued that "you can never have enough power in a Porsche engine" and that they should go for S specs. Peter Eckert, however, argued that since this was a matching numbers car it was more important keep it original.

I would certainly have chosen to go for S specs.

Depends on the specific car. For instance, the performance difference between my 2.0 E and a 2.0 S are basically undetectable from 0-60. And the 2.0 S hasn't nearly the life/torque my car has below 5000 rpm. The price to go from E to S could be as much as $10,000. Worth the money? Not in my opinion. Plus, who does the work? Did they do it right? Or did they turn the engine into a rolling grenade?

If you really want the best, most economical upgrade, drop in a 3.2. Power + Torque = :D Like the 3.2 in my 914/GT clone. Awesome baby.

I think it comes down to the model being restored and its original condition. 1970 and 1971 Ts are pretty common, so collectability is not a crucial factor. But I assume if one is restoring a 1964 901, you do not put S cams on it.

I've owned my 911 for 20 years and have kept it almost totally stock -- in another 20 years, numbers-matching, stock early 911s will be so rare that it will command more money than a modified 911.

By the way, those are enjoyable videos on the 911 restoration, I just wish i understand German.
SCOTT