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.

I like the subtlety of the 0/3/6 dB switch. The original 8 dB boost is very prominent, it adds a strong accent on top of each note that is too strong for my ears.
 
The 6 dB boost adds a somewhat weaker accent, but still an accent. The 3 dB boost adds a nice sparkle when the filter is fully open, and else just a gentle 'bump'.
 
I think I could live with just a 0/3 dB switch.

My custom is going to have a 3 position Q at 0/3/6. The upgrade is $150 retail. Like others have said, 8db is a big amount and to me the Alembics already sound so good flat, that I only do subtle EQing so smaller changes was the way to go for me.

It would be my guess that the effect from the amount of db boost of the Q switch probably varies with how you have your rig set up (and probably with other factors such as the wood combinations in your bass) (and of course with personal taste).  For instance, I can remember that before I got my first S1, the 8db boost on my Spoiler seemed like a lot.  However, now on my two main basses, the bridge Q switch stays on 9db; I never back them off.  I imagine it has a lot to do with how my SF-2 is set up; but I'm sure part of it is personal taste as well.

Mica, could you make my bass in time with additional bass and treble knobs and 3 way Q toggles?? It's important to make a decision.

Yes, we will be able to accomplish both requests with the time available. Tony can make these modifications without having to book time on my dad's workbench.  
 
I will make a control layout for you to review in about a week.

From your last email I understand that you want the peghead arranged with a 2+3 pattern so the B+E strings will be on the left side and the A+D+G strings on the right side.  
 
Please let me know if I understood your request.

Yes, For the Quality of Low B string~!!

Both of your examples are of 4-string basses, which have smaller pegheads than 5-strings. In this example you can see a 5-string smaller Crown peghead.

Okay. It's good. Thanx Mica

From the tummy contour thread, you're asking to change from abalone inlays to the standard mother of pearl. Let me know if I've understood this correctly.

Yes, Correct.
And about the shape of Peghead, I want to get the new Crown Peghead shape.
What I mean... the old type Crown Peghead is somewhat bigger than new one, right? I want to slim Peghead shape like in Bird of Prey. Of course, not including head omega carving option in Bird of Prey.

And I add my opinion about the additional swithes in the Pick-up location and Additinal switch page. please check it, Mica~

I think the Ragging bass Head style is good example,too.

For more on the peghead, please see the peghead thread. Thanks.