Tom,
Not enough.
However, I was also speaking for Par 4s and 5s as well. Depending on the design of the hole, that could effectively add a shot to the hole...
For course rating, distances absent elevation/altitude/roll adjustments for the scratch player are 225+25=250 off the tee, then 225 off the ground thereafter.
Thus par 4s over 475 might have this "extra shot" effect, and it would take a par 5 over 700 to achieve it.
Obstacles can effect this as well - but we're just talking pure distance here.
So yes, the way courses are being laid out today, there will be quite a few holes over 475 that courses call a par 4. And given the way the ball goes today, it's very realistic.
Just do understand that in these cases, again the net difference isn't going to mean very much. John V. can quantify this much better than I can, but think of it as a very easy par 5 as against a very hard par 4. Your scoring averages are going to be pretty close, right? That's how it's going to work out for course rating also, more or less.
Thus it is just a curiousity.
One more thing: don't get too caught up in these course rating distances being "unrealistic." Remember if they're the same for everyone, it really doesn't matter much what they are. These numbers just need to be the same course to course to make the handicap system work.
TH