I found I needed to type this story a few times in a row today while giving advice to other runners.
Do I just take out my orthodics or 'just' buy Vibram Five Fingers and take off running??
After 1.5 years I can run a competitive distance race with NO shoes. Although that may not be a goal of yours, it's an indicator of foot strength. As a kid I had such flat feet that the outside and inside of my feet looked the same. Now I have a strong-looking raised arch. It's a wonderful thing but it took a loooong time. I'm not sure I took the most direct path to achieve this.
There are two approaches here and one will better suit your race-schedule, fitness goals, ability to be patient, etc. There's two ways to approach your goal of building foot strength.
1.) Keep your current running (or training) schedule with minor alterations and wean yourself slowly off inserts, raised heels and cushioning over time. Example: Going from a 10mm raised heel shoe to a 4mm, to a 0mm.
--The downside of this technique is that you have no real motivation to fix your form/balance. One may develop some intermediate issues - such as, it's hard to have a fast cadence when your heel is raised, it's hard to know you're mid-footing landing when you have ~0.5" of cushioning.
2.) BAM, press reset and run (or train) ONLY 5 MINS barefoot twice a week for a month, and increase frequency slowly. then add a zero-cushioned protective shoe (like Altra Adams, Merrell Trail Gloves, Vibram Five Fingers, BF Inov-8s etc.) when barefoot, only run on hard smooth debris-free surfaces. concrete or asphalt will give you indicators that you're doing something wrong (like over-striding-aka heel-striking, or pushing off too much)- either of which would cause hotspots on the soles of your feet.
--The downside of this technique is that you may affect your current fitness level. BUT this is easily overcome by substituting your previous intense running sessions with rowing, swimming, cycling to keep the engine strong. The unshod running will build foot/leg muscles that have been asleep since your first heavy toddler shoes.