Tube Rolling Experience with the Herron VTSP-1A

I'm interested in actual experience with this preamp. I have been generally very pleased while using it with the stock EH 6922 tubes, coupled with the Herron M150 amps. Keith Herron originally designed the preamp to achieve neutrality with the stock tubes, but I would be very interested to learn from the observations of those who have substituted tubes. Describing the sonic character of the change would be most appreciated. Also, recommendations for more moderately priced tubes (less than $100) would be helpful.
I don't know if my question is too elementary or too specific. Maybe there is little experience with tube rolling in this preamp. I don't want to sacrifice neutrality, but what I have read about the later preamps Keith has designed would suggest possibly that they're fuller sounding. I'm not so naive as to think that replacing the tubes in my preamp would result in that kind of signficant upgrade, but, again, I would be interested in anyone's related experience or recommendations.
Thanks again,
Since the Herron VTSP-1A produces a very natural sound, i dont see the need to make a tube rolling. The lows and highs are perfect on it, it sounds even better than my previous Bryston's.
Thanks for your reassurance about the Herron equipment. Perhaps others out there have a similar view and that's the main reason for lack of response.