Thanks a lot, Corlan and Matt.
Corlan, I already use the DK-21M Magnifying Eyepiece (magnifying 1.17x).
The DK-17M Magnifying Eyepiece (magnifying 1.2x) doesn't fit my D300 body.
Maybe I should just see it as a convenient excuse for upgrading to a larger and brighter viewfinder FX format camera and at the same time adding the DK-17M Magnifying Eyepiece.
On the other hand I would prefer to save the money for a 4/400mm VR tele lens for birding. Or a 5.6/400mm VR. I wonder how many more years I will have to wait for one of those.
Not exactly a street shot, but just to illustrate what we are talking about