Huh?
Here I was just about to agree with Chessrock, and he changed his position.
First -- for the original question, I think the VMP3 output can be connected to something that wants either a -10 or a +4 input (yes, it could be connected to a -10 balanced or unbalanced input or a +4 unbalanced or balanced, if that's what you happen to have). Just adjust the gain and look at the meters on the thing you're connecting it to.
The only limitatation is the amount of gain. The maximum gain is 66dB, so if the signal produced by your mic is less than -62 dBu (.0006 volts), you won't have enough gain to produce a +4 balanced signal. When you connect the VMP3 output to an unbalanced input, you lose about 6 dB (i.e. half the voltage, since you're grounding one leg of the balanced connection), so you'd need a mic signal that's at least -56 dBu (.0012 volts) to produce a +4 unbalanced signal.
According to the manual, the maximum output is +22 dBu (balanced) or +16 dBu (unbalanced), so that's not a practical limitation.
It doesn't "automatically" switch from a nominal +4 to a nominal -10 output when you plug a TS plug into it. It just loses 6 dB (half) of the signal. The difference between +4 dBu and -10 dBV is 11.79 dB (a factor of almost 4).
Second -- on the side issue, which the original poster didn't actually ask about -- when you do have a choice between a +4 or a -10 output (which you sometimes do, particularly when dealing with something that doesn't have a pot to vary gain or to trim the output level): I would have thought the correct approach would be to use -10 when you're plugging the output into something that expects a -10 input, and +4 when plugging into something that expects a +4 input.
Sor far as I cant tell, there shouldn't be any significant difference in the amount of ambient room noise. Say you've put the mic in a room with a singer who's making a 70 dB SPL racket right next to the mic, while there's also a refrigerator making a 45 dB SPL noise (measured at the mic). There's going to a 25 dB signal-to-noise ratio between them, no matter what you do -- at least so long as you don't compress or expand (or gate) the signal (compressing will generally make the signal-to-noise ratio lower, and expanding will make it higher).
If you adjust gain on the VMP3 to produce a signal that peaks at +4 dBu, the ambient noise will be at -21 dBu (.07 volts, if anybody's counting). If you adjust gain on the VMP3 to produce a signal that peaks at -10 dBV, the ambient noise will be at -35 dBV (.018 volts). In the end, on tape or disk or a playing over a speaker, it'll all come out the same.
Caveat: it's possible that the VMP3 compresses the signal somewhat at very high gain settings. I don't know that it does, and it really shouldn't, as long as you're within it's rated limits, but it might. Another caveat: if you crank the gain to produce a +4 signal, you will get more electronic noise from the preamp itself.