Disclaimer: I am a BikeFit instructor (so I teach foot/pedal interface stuff, including wedges).
The answer is "it depends, and it's complicated." Probably more complicated than it should be to do something as simple as ride a bike, right? lol!
Most of my customers come to me because of pain issues. There is a lot going on at the foot that we have to at least consider as part of a bike fit. It is my duty as a fitter to understand what your primary concerns and issues are on the bike and focus on those first. A lot of problems can trickle up from the foot. I think it's also my responsibility to be objective and not necessarily be a big "fan" of any particular tool. I don't want to be a cabinet maker who is a fan of sledgehammers. I'm a fan of the end results.
The lower extremity is a key area where we can gain efficiency in the fit process. The stabilization and alignment of the foot, knee, and hip are all important to ensure efficiency, comfort, and injury-prevention. Our knees are the canary in the mine. The knee is a single plane joint, and we don't want it to be making lateral movements. That's going to require additional stabilization, which is additional work for the muscles that aren't propelling you. The pedal stroke is an amazing neurological sequence - think about how each of the muscles have to fire, in sequence to move your foot around that 330-350mm diameter circle. Also, think about the muscles that have to stabilize that movement. There's a lot going on there. The small muscles in the lower extremity are relatively oxygen-hungry - they require a lot of oxygen for their size, but really don't provide a lot of power to the pedal stroke. So, it's best to quiet them down and make them relax by ensuring they have a stable relationship to the world around them. So, what can we do to ensure that stabilization? Provide a stable platform.
The pedal is a horizontal surface, and unlike most horizontal surfaces our foot interacts with, we're locked into it. That's just unnatural. Most people have a varus cant to their forefoot, meaning that if you look at it across the transverse arch, the line from the fifth metatarsal joint to the first metatarsal joint travels at an upward angle. This is one angle as part of the chain from the foot to the hip, and it is relative to the rearfoot and lower extremity. I've measured this angle to be as high as 28 degrees, with most people falling in the 10-20 degree range. Now, we're not going to throw in 28 degrees of wedge and call it good. The most I put is in 3 degrees.
Wedge is one of many tools to factor in here. I determine how if and how much wedge is appropriate based on rider feedback, my observations, and accepted practices, in that order. I've had people who, by convention, should have 3 degrees of wedge, but don't end up with any.
Also, when most people think "wedge", they are thinking specifically about a cleat wedge - the angled plastic shims that go between the cleat and shoe. These will cant the entire shoe, which is generally fine, but not always. Once again, it's all about providing a stable base for the foot. Heel wedges, insoles, and in-the-shoe wedges can all be appropriate in the right situation. Cleat placement is key, both fore/aft and laterally (stance width). Leg length and heel rotation also affect the way we interact with the pedal. Another big one is crank arm length. I often see people with poor hip mobility, a hip impingement (FAI) or other impingements (aka "guttus interruptus" - their belly gets in the way). When I say "poor", this means "just tight enough to limit movement at the top of the pedal stroke." Probably not even noticeable when they walk or run, but force them into a 350mm diameter circle (for a 175mm crank arm) and the bad things start to come out. This is one reason why we sometimes see knees coming out at the top of the pedal stroke - if the knee can't go up any higher, where else will it go? Either the pelvis/upper body rocks, or the knee goes out laterally. Saddle height and crank arm length are both important factors here (and sometimes, a delicate balance).
So, I babbled on a lot there, but I hope that makes some sense. For the TL;DR read crowd - wedge is useful, but one of many tools in the tool kit. I think you're going to get a mixture of reactions from fitters here. Some love this stuff, some think it's snake oil. I'm a skeptic of everything but will consider everything I have at my disposal, and I'm always seeking ways to improve the process - from high-tech to back-to-the-basics analog simplicity. It's all about finding what the rider and I feel is the best solution for their problem (without creating a problem just so we can solve it). My bike fits are a partnership, and my customers become my students and are hopefully more well-versed in bike fitting and more self-aware after we're done.
To specifically answer your last question: It depends, and it's complicated. ;) You could benefit from insoles, wedge/cant, or maybe nothing at all. If you have pain, you probably need something.
Travis Rassat
Vector Cycle Works Noblesville, IN
BikeFit Instructor | FMS | F.I.S.T. | IBFI
Toughman Triathlon Series Ambassador