You feel the same after 5 or 7 as you do 2.
The key is the medicine each evening. At the 16's their are lots of "Doctors" with bottles of Don Q medicine. The dosage can be a problem if you're not careful.
The week goes very quick.
As John mentioned there is a lot of competition among some very evenly matched sailors in large groups. Top 10, next 20 and so on. Set your personel goal and go have some fun.
Once you've done one it's hard to stay away. My first major event was the 93 H16 Nationals(same as John). I have read his account of that event and smiled at having similar memories.