And then there are the large numbers who put various versions of the 'Realist' pickup under the E-side bridge foot... copper foil, some sort of gummy, tar-like tape between the folded copper, and most of the bridge's pressure resting upon less than 1cm square (a lot less!) of peizo elements inside all that. Without adjusters, these pickups (and a few copycats) are almost guaranteed to harm proper fit to the belly. Even with adjusters and the relative flexibility they bring to the foot contact, the acoustical through-put is dramatically impacted, at least in theory. In most installations I've seen from other shops, one can easily slip a business card underneath more than 50% of the bridge foot/pickup, which, considering that the contact between bridge foot and the area of the belly directly over the bassbar is rather important (understatement), should be alarming. But hey, it's a great pickup in the 200 ~ 1,500Hz range, so whatever, right?
In my experience, adjusters have never harmed sound. In some cases there has been a noticeable improvement in response, possibly owing to the increased flexibility of the bridge legs, a subject upon which Chuck Traeger long ago published an essay. He admonished that EVERY bass should have adjusters. I don't quite agree... but do accept that every bassist needs to adjust bridge heights sooner or later. I'd rather see neck adjustability more broadly implemented, using sound engineering and simple, repairable mechanisms, perhaps with some sort of emergency impact failure element built in for when bass scrolls meet with doorways at high speed. But that's another subject.
If you are finding that bridge adjusters do not work for your sound, fine, and if you are patient enough to deal with shims that fine too. Gary Karr carried several bridges with him on tour for decades, putting in the one for a local level of humidity (arching rising or falling with the weather) or perhaps for differing string heights. More recently he uses an adjustable-necked Ham bass. Gary's students and their students in turn are all discouraged from using adjusters. Gary has long held that adjusters are an abomination. My experience with many hundreds of basses does not support this perspective, but again, to each their own. Many of those students suffer from inconveniently high and low action, at different times of year... Not much I or other luthiers can do about such a predicament, as they are equally unlikely to want shims.
In the odd case where shimming is wanted and needed, I use 0.5mm maple veneer and just stack it up until slightly over the height wanted, then re-fit the bridge to the belly, as the stack of veneers inevitably alters the fit. And fit to the belly on both feet is critical to proper sound, period. Unfortunately, relatively few luthiers seem either capable or interested in fitting feet to belly, so I put together a small page showing a before/after set of bridge feet and the basics of how I correct such disasters, here:
http://www.luthier.ca/tutorials/brid...e_fitting.html
Perhaps you are not so worried about fit, considering your shims are not glued. And on occasion I have fitted loose shims, when a client is unsure about exact height and wants to try a few things before committing. Provided the veneer layers are thin enough and therefore flexible, there's nothing wrong with this. Not ideal for vibration through-put but not the end of the world either, as it's easy to remove the shims. Of course, as someone else stated, one ought to be comfortable with setting the soundpost properly when undertaking such experiments.
