Andy:
The heart of what you said was 'should I go to a good G U I T A R tech . . .
First, I know great guitar techs that are at a disadvantage when it comes to basses
Second, I can easily imagine that in London there are surely qualified people to handle your ALEMBIC.
The links back to the previous posts will tell you all you need to know. If the once-over-lightly works for you every couple of years, great. Get it dialed in for your usual strings and have at it.
But believe me, ALEMBICS are the easiest instruments upon which to learn adjustment. The adjustable nut, the bridge, the dual truss rods, coupled with the quality of wood and assembly, make it a breeze to learn yourself. If you have very precise hands and touch, teaching yourself means that every time you try a new brand of strings or different guages, you can dial it right back where you want it. If you can feel these tiny differences, doing it yourself will save you a fortune in trips to the tech. Plus these basses are solid enough NOT to require a lot of touch ups once you get it where you want it.
If you dive in, believe me, your first couple of trys you'll make it into a real plank. Then it will begin to come to you as you slowly find your way back, the movements and the interaction of relief, string height, nut height, etc. will crystallise in your head, and, voila!, you've got it. This is the normal progression as you learn this.
I have never enjoyed playing more since I learned to perfect 'my' setup myself. Most people who try it have NEVER felt action on a bass this nice. And I'm no longer at the mercy of strangers who I just can't seem to explain just where I want it.
Enjoy, but don't say we didn't warn you . . . you will pull your hair out for a while at first!
J o e y