I agree with John - most add color and character. All that I have worked with do in some way.
Another consideration... For loud rock, you may only need to add 15-25dB of gain. For purely acoustic, maybe more like 40-55dB. I'd expect the amount of gain to influence the sound character, but I don't think it has been discussed much here over the years. There is also the question of how hot the pre-amp is being driven on the inputs and outputs. Since certain harmonic distortion can sound subjectively good, there is the question of whether a particular pre-amp must be run in the 'sweet spot' to get those effects.
Recorders also have 'sweet spots' in regard to dB input levels and gain settings. We also know that some recorders distort at certain input gain settings. Some of that distortion is very obvious, yet quite a few folks here argued for a long wihle that it didn't happen. So if obvious distortion is a point of contention, where does that leave more subtle impacts on sound character? I don't think we've ever really answerd the question of whether the 7xx sounds better with the line in run at 0db or -6. I always ran at 0, some run at -6.
I think the v3 is the most transparent portable that I own, but it rolls off the low frequencies a bit. Either that, or everything else is bloated on the low frequencies. It'd be interesting to hear what Grace has to say about that. I've done quite a few comps with my Rmod, the predecessor of the nbox. It is very transparent. The DAV BG1 is comparable in detail to the v3, and does not roll off the lows. But it requires 110ac, so it is more of a chore to run in the field.
In my testing, the sonosax "smears" detail. The behavior of the aerco probably depends on which transformers you have. Mine do not add gain. It is somewhat warm, very detailed but not as detailed as the v3. I greatly prefer the aerco over the sonosax. Though I don't record from the section at phish shows, where some people love the sonosax.