I am a new owner of a 302B and thought I'd put in my 2c on the subject.
The unit I purchased was a "modded" one through Underwood HiFi. I can tell you that the service from them is unbelievably great. Without having a comparison to the non-modded version, I cannot speak to that. However, I can say that the insertion of the 302B in my humble system was like night and day.
It replaced an Electrocompaniet ECI-4 (ss integrated 120WPC). Anyway I just wanted to get back to tubes and the 203B seemed like a solid option. It was. The increase in detail was astonishing right from the start. And this was before the tube rolling (now a BRAND NEW HOBBY for me).
The soundstage opened up compared to the ECI-4 and the power differential between the two amps was immaterial (it's a pretty small room anyway).
On to the rolling -- First in went a pair of Mullard CV4024s in place of the 12AT7s. Oh my. The soundstage widened. The imaging became dramatically more precise and the little harshness in vocal frequencies (likely just at the cross-over frequency of my B&W 805's) went away. What a difference. If I made not other changes to the tubes this improvement was all I could ask for. HOWEVER. . . next came a pair of 1961 vintage Sylvania 12AX7s. Well, no more brightness at all at the highs (something possibly in the Mullards makes them just a touch on the zippy side. The imaging remained but the soundstage stepped back a bit.
Last but not least was the insertion of a matched quad of Svetlana EL34s. Back came the soundstage into the room once more and the silky tones of the mostly female vocals I listen too emerged in full throat. The spookiest listen to date is Jane Monheit doing "Over the Rainbow" in which she opens from dead silence into a capella -- really hair raising.
Anyway, now that the intial round of rolling is over (like I said it's now a hobby) I am changing out ICs to see if I can get even more out of this wonderful little amp. My hat's off to Walter at Underwood Hifi for coming up with the mods and for the incredible service. Even though they are across the country from me, I will use them again and listen to the recommendations from there as well. As for the 302B -- I couldn't be happier. Actually I suppose I will be when the new ICs and DAC go into the system.
System Used (before all the cable changes with upcoming mods ID'd:
Parasound CDC1500 (just as a transport (Nakamichi coming in)
Audio Alchemy DTI 2.0 (AA DTI Pro 32 coming in)
Audio Alchemy DDE 3.0 (Channel Islands VDA-1 coming in)
Cardas IC's (Bolder Cable and RS Audio coming in)