Of course, it remains to be seen how this effect scales in practice, but I believe the initial usefulness will be more in continuous moderate thrust over a long period than a top fuel nitro type of drag race spaceship.
50 kilograms of thrust over a week on a smallish spaceship puts it to astronomical speeds. Even 5 kg of thrust over time is huge. To get propellant to space is hugely costly. The way we do it now is a very short burn, and then coast the rest of the way. Lets suppose the burn gives 1000 kg of thrust. The 5 Kg starts slow and keeps adding up. Before you know it those 5 KG second after second hour after hour day after day can yield orders of magnitude of orders of magnitude of orders of magnitude ad infinitum more thrust than chemical propellants. Wont get you out of a planetary gravity well, but once out there WOWSERS.