Stiffer will "help" with control but making sure your turns and skills are Solid is a prime way to help with control issues. I started out the same way always looking to my boots to help with control. Went as far as using the Burton Driver-X but later I figured out what helped out much better than stiffer boots. I took a clinic at Park City when it came to snowboard skills and Freestyle progression. At first I thought it was going to be a waste of a day but it turned out that it helped me to become a solid rider. I have big calves, but not wide feet, but today my MAX stiffness range for resort riding is a 7. I use two boots and switch back and forth from my 32 Lashed stiffness rating if about a 5. And my Burton Grails with a stiffness rating of a 7. I use my Lashed with my Skate Banana and my Grails with my TRS. The only time I break out the Drivers is for Backcountry Pow. And then I'm using either my Rome Mod or my Burton Fish. But it's rare when I use either due to living on the Easy Coast now.
What I'm trying to say, and I'm sorry if I hijacked this thread, is save your cash. The boots can only help so far with board control. Try these three things first and if they don't work then go after the stiffer boots. Tweak out your bindings, rotate your heel cups, try a newer set of angles, check that your boots are centered in the bindings, relocate your ankle straps to a higher position. If your bindings are older check out upgrading those first. Next widen your stance and if your bindings can be set up for canting try 3 degrees to take the strain off your knees. Finally and I know this idea sucks, take an advanced skills class and tighten your skills. It helped me a lot, also you could try looking at a new board too but with not knowing your current setup that could be a waste of time.
Just stating an opinion and some things that improved my skills when stiffer boots didn't seem to help anymore. Sorry so long of a post.