How do NW and DL miles relate to each other in value? That is, are the award charts already fairly aligned? Is the access to OW partner award inventory equal? Booking fees and other oddball rules/fees equal?

Without knowing that it's hard to say whether burning NW miles now is advantageous. They may or may not be a good value at 1:1 conversion to DL.

Take United for example. I would value 1 US mile higher than 1 UA mile for two reasons: (i) several very attractive awards require a lot fewer miles on US than on UA and (ii) US does not Starnet block like UA does - a major factor that makes it difficult for UA fliers to book the best award seats available in the system, even when the operating carrier has made them available.

(A minor downside is that US would hit me with some junk fees that I don't have to pay UA as long as I'm at the 1K tier.)

Anyway, I don't know the situation with NW but without more information it's hard to say if the 1:1 conversion is a good deal.

When my TW miles converted to AA 1:1 I thought it was a bit of a mixed bag. I actually used the TW 15k award on very short, expensive nonstop flights because it was often available at the last minute with no booking fees. DFW-STL, for example. That flight would have a $600 R/T walkup fare, but I could still call TW the morning of departure and get it with 15k. So I miss that, but I also like the OW alliance and AA's route map in general...