Wheel spacers vs. Backspacing

At 3.5-4 inches of lift and 31x10.5x15 on stock alloy spoke country weels, I only rub on my LCAs at full turn. This is not so bad when I have ATs on, but I recently got a set of pro-comp MTs with FAT sidelugs and at full lock I feel like im going to rip something off.
I am eventually going to get 2 sets of wheels with 4.5 inches of backspacing (one set for road, the other for trail), but right now at only 10.5 inch tires, It doesn't seem like its the most important purchase right now.
What about wheel spacers? Not the super nice 200 dollar a pair spacers, but the cheapie stamped steel ones you use with longer wheelstuds. Don't these serve the same purpose as those nice billet spacers, or backspacing without the extra rim width?
If they are an ok idea, what width is safe/effective. I think they get as fat as 7/16 inch. Thanks for the input. Would this be enough (or too much) to get my tires off the LCAs?

Yes, they would serve the same purpose. I would not go more than 1/4 inch, because you'll be putting the wheel studs into a shear/bending condition that they weren't designed for. You can also control the rubbing by extending the steering stops on the knuckles, although that does reduce your overall turning ability somewhat.

Look under your truck from the front. On the body of the knuckle you'll see a bolt with a locknut on it, threaded into the knuckle. The locknut is welded to the bolt, but you can remove it and shim with one or two flat washers and that adjusts the maximum amount you can turn.

does increasing backspacing not mess with your turning radius a bit too? Also, do you think that 1/4 inch would be enough to stop rubbing? Or would a combo of steering stop adjustment and wheel spacers be my best option>?

Why not just get rims with 4" back spacing? Unless you already have the second set of rims and tires.

Sorry, misread your post. I thought you were rubbing with rims with 4.5" backspacing. Me bad.....