When you go to the FCC website, after you bring up WDEL in am query. click on applications list, then click on the most recent, from this month. When it opens, go to the bottom of the application, where exhibits are, and within them you will see the 5kw current vs. the 10kw proposal. Basically it loos like an better signal to the Northeast (Philly area), to the west into Cecil county and Northwest a bit.
I think they want to improve there signal against electrical interference, as well as coverage in the Newark and Elkton area. Cecil County is a part of the Wilmington Metro, and since a good number of people in that area travel to New Castle County to work and shop, plus with the housing growth along the Rt. 40 area, this makes sense.
The cost of the upgrade includes not only a new transmitter, but they will probably have to replace their phasor array, since the old one can't handle the doubling of power. If HD radio ever takes off, the fact that t hey are on the WSTW HD3 could help. I would love to see them add WDEL to the HD of WAFL, giving them better coverage downstate.
Hope this helps.