Shim-
The upgrade from 2-pos to 3-pos Q switches was $150 per switch two price increases ago when I ordered mine. It should be somewhere between $150 and $200 today. Personally, I can hear a difference between the extra settings, but don't find them significant enough to matter for live use. If you're planning on recording, they may help, but you should then also have access to more EQ options in the signal chain, making them less necessary.
I do warn you that you need to get simple and come to a decision. Adding anything that is custom beyond Alembic's regular available components will add significant cost and time to your project. I don't believe that they just solder in a different resistor or cap to change values on switches with some testing and measurement.
If you want maximum flexibility under your fingertips when you play, go for the bass/treble knobs and the 3-way Q switches. By the way, the standard 3-pos is 0/+6/+9.
I would probably go for the bass/treble knobs over toggles in either case if I were planning to add that function. The 0 and +6 positions are just as repeatable as with the toggles and you do get a bit more flexibility. I find the +6 setting on the bass control to be a bit strong and believe that you would benefit from the flexibility there in particular.
I would also say that control is great, but so is an attractive bass with great top wood. The more switches and knobs, the more I personally feel it impacts the natural beauty of the instrument. I don't know how you plan to use the instrument, so I don't feel comfortable making a hard recommendation for you. For me, I would start simple. My first add would be the bass/treble knobs and then, if finances allowed, I would go to the 3-pos Q switches. I would also consider some custom wooden or shell-capped knobs if I were adding that many controls to the instrument.
