I should have just put in a separate thread about the rear wheel! given that all the comments have been about it. I added some more description about the rear wheel (which has its own photo gallery, linked from the main photo gallery and from the wheel picture in this thread).

Lectron: where does one get a spoke head driver? What I did with the washers is to
a) bend the spoke such that it pulls the head mostly into place and deforms the washer
b) use a pointed steel punch and a hammer to drive the spoke heads even more to seat flush with the flange.

So I think what I've got is pretty good. But a spoke head driver would probably just be easier.

And yeah, washers do help in most wheels (except Phil and Dura-Ace and a few other types of hubs where the spoke holes are designed small enough so the spoke seats ideally - and even then washers make sense if you build with spokes that are 15g (1.8mm) at the head.
And they add virtually no weight, and only at the hub where rotating weight matters much less than at the rim.