Hi Mark,
From my experience with BAT I do find the SE models to be more accurate and true to the source. They also have better extension at both extremes, dynamics, with better resolution of detail. All very good things!
I would think that VK32se gives the user plenty of control tailoring the sound to one's taste and system with the other options in tube choice. I advise going with the SE version.
Word has it with regards to performance that the 51se vs. 32se scenario is a give and take situation, where the new 32se has a more natural organic rendition of texture/timbre of tone. I don't know this from first hand experience.
I agree with your choice of sticking with BAT as I also have found their sonic virtues to be so well balanced and on target with my taste on how I hear sound.
As far as BAT the company? I cannot praise them highly enough! Good luck with whatever you decide on.
Best,
Tom