Hey, wait a second..I love var. vinca major. I'm just lousy at keeping it inbounds (inside MY yards).
In a needy site it serves to brighten under trees and the larger flowers are lovely, wish they lasted longer.

If you can resolve to be good about keeping it not only pinched back to a small area but also thinned out so it doesn't rob the moisture the maples need I'd leave it.

If you are at the point you're tired of the constant maintainance try a spring trimming and then painting the trimmed with (a slightly diluted?) brush killer. The object being the weakening/death of the vinca roots and all but not the harming of the maple tree roots.

I fear that if you try to pull out all the vinca roots, you will indeed be disturbing the young maple roots at a time when they are going dormant. You might then get root rot of the maples and for young trees without an extensive root system that could well kill them.

If you try to pull the more distant vinca(distant from the Jap. Maple roots) you might encourage the vinca to set more root closer to the trees. (dammed if you do,dammed if you don't).

Ideally, the best solution long term involves lifting the J.Maples(get help and take a lot of soil width with the least amount of soil disturbance/breakage) after they are leafless and then clear the area of vinca roots.
If you like the vinca, clear a 4' dia. circle around where you will plant each maple and sink a root block on the perimeter.

Keep in mind that the maples have had a root cover of vinca vines so when replanting give them just a touch of light fluffy (pine straw?)mulch so the top most roots don't get sunscald. Draw back that mulch frequently and keep a check for voles.
Remember too that the replanted maples have more access to moisture without the vinca competition so you might want to plant them a touch higher in the soil.

Thanks, Dottie! (I don't feel quite so guilty now! ;-D) Will take all of your excellent advice... voles... ugh!!