"Using median size as a reference it's perfectly possible to fit four ping-pong balls and two blue whales in a rowboat."

Median is an accurate representation of only the most ideal samples.
The main selling point of Median Node-Fu and Median Node-Fu Product is that you could check this for any user at the cost of, at most, two votes. This selling point is irrelevant to a behind the scenes process as it is not limited in the number of write-ups it can check for reputation.

Here is my recommendation:
Divide the reputation sorted list of someone's write-ups into N sections. Find the reputation of the write-up in the middle of each section. Mutiply the value of these midpoints by 1/Nth the number of write-ups. Add these products together. The resulting sum is someone's contribution to E2.
Sound familar? It's an algorithm for calculating the area under a curve.
As you may recall from calculus, the accuracy of this measure increases with N (specifically in this case accuracy increases as N approaches #WU)
Node-fu would be calculated by averaging the the values of the midpoints. These methods can be refered to as MpNF for Midpoint Node-Fu and MpNFP for sum E2 contribution.

Some interesting things you may not have noticed

  1. When N=1 this method gives you MedianNFP and MedianNF
  2. When N=#WU this method gives you MeanNF (I.E WNF uncorrected for C!)

  • As has been noted MNF and MNFP are generally more acccurate for users with large numbers of write-ups (due to a more ideal distribution of reputations). This is also true for MpNF and MpNFP. However, the expected accuracy of MpNF and MpNFP increase as N-->#WU... therefor noders with fewer WU can expect higher accuracy. The overall result is that MpNF(P) is generally accurate for all users
  • The value of N can be the same for all users. Thus there is no greater computational overhead for figuring the MpNF of a Lvl10 noder v. a Lvl3 noder.
  • The value of N can be adjusted for different levels. The tendency for expected accuracy to decrease can be corrected by increasing the value of N for higher level users. Because the number of users drops off as level increases this would also not produce a significant change in computational overhead between user groups.
  • As with MNF and MNFP, skillfull selection of the value of N will allow radically up- and downvoted write-ups to be ignored in the calculations.
Random other considerations:
  • Two write-ups both have reputations of 1. One has (+35/-34). The other has (+1/0). Have they contributed equally? Do they both have equal Node-fu?
  • When the value of recieving C! or the number of votes alotted is changed should XP be recalculated to reflect the changes?
  • How do you encourage voting but not vote dumping?