As much as it is really important to see "how the sausage is made" and get to DC to talk to POs, there is tremendous value in serving on a panel even before you travel to NSF. If you are serving on a panel that you have or will submit to, it is critical to read every proposal while thinking "what does my proposal have that will get it selected ahead of these?" I am currently reading proposal after proposal of incredible science communicated clearly. There's a lofty bar in this panel and I am getting a much better feel for where it is at.
It's both energizing and terrifying at the same time.