spigelia marilandica should be considered a woodland treasure. i could not see where it would ever be considered invasive. i understand the clumps are rather slow to expand in the garden. don't know about transplanting since i ordered mine from a nursery and planted in late winter.
if i were transplanting, i would attempt to get as large a soil mass as possible to avoid disturbing the roots and keep it watered well this first growing season.
i also grow lonicer sempervirens (native red honeysuckle) and have yet to find one popping up in the surrounding area. this is a much better plant to cultivate than its asian cousins - now, they are invasive!

Thanks Jeff. There is a fair amount of it, and I'd like to get some of it closer to the house to attract hummers. I may try to transplant a clump. I've also seen both growing close together in a wooded area where I jog. It's next to a trail a neighbor cleared for access to a man-made lake. I didn't realize the "pinks" were considered a treasure. And we do have plenty of it's asian cousin! But I love the smell this time of year.