The problem with imperializing something like a wit is that a lot of the original character is the light/refreshing nature of the style. You could certainly add more wheat malt extract to a kit, but I’d also include ~1 lb of table sugar to try to keep the beer crisp. I would up the bitterness proportionally (if your beer is 50% stronger, add 50% more hops/IBUs), but I would leave the spices as is. Personally I’d keep it around 7% ABV, but you could certainly go higher if you don’t mind losing that lightness. Make sure to pitch enough yeast, give it enough oxygen, keep fermentation temps down, and let it have enough time for fermenting/conditioning.