The p.o. of my Bronco did an upgrade, but with an additional light.
If you think about it, the problem with the stock dome light is where it's located, way up on the bottom of the wiper motor housing. Having it brighter will only help so much at getting light into the interior.
So, the dyed-in-the-wool Bronco tinkerer/restorer made a simple L-shaped bracket for the rear of the ceiling right above the liftgate. He then installed an inexpensive rectangular fog/auxiliary light (like you'd put on your front bumper) which points straight down at the cargo area behind the seat. It's wired to the same circuit as the stock dome light and they work in tandem.
It really does a great job at lighting up the whole interior, and even works when loading stuff into the back (p.o. used the Bronco for hunting and fishing trips). I can't imagine the whole set-up cost more than $20.