In the short stretch I had the WA-2A it worked extremely well on all three instruments you list. We liked the Warm better on an acoustic guitar than an original LA-2A - on that song anyway. It is killer when it works. However, (and it was not an exhaustive testing) I would think the Pultec would be a better general tool. 2 tubes are enough to get that tubey goodness and one of the tubes in the WA-2A drives the optical T4 unit and is not in the audio path.
Even with 3 tubes (and transformers) it is important to note that most of the warmth and saturation comes from how you use the unit, rather than tubes and transformers being a magic bullet of fairy dust. The sound does change between a transformerless/tubesless design and a unit that does include them. More 2nd and 3rd order harmonics as well as humps and frequency emphasis applied to the sound passing through. But it is the driving of those non-linearities that "adds" to the sound and you learning - for your own style of sound - how much on each instrument you need. Two guitarists can play the same notes, but if one knows how to play the notes lyrically rather than mechanically and in the correct idiom, she will sound better.