You're getting more lumens compared to the 35 watt kit but think of it this way. If you had halogens, you would have anywhere from 900 to 1200 lumens. If you have the 35 watt kit, you're going up to 3200 to 3400 lumens and with a 55 watt kit, you're going up to around 5000 lumens.
Also, when you go for the 55 watt kit and choosing color temp, the higher wattage kit is reducing the color that you may be going for. Example: an 8000K 55 watt kit is going to look like a 6000K 35 watt kit. So if you wanted a blue tint in the 55 watt, you would most likely need to go with the 10,000K so that it would match what the 8000K 35 watt kit would look like in color.
For the money, going with a 35 watt kit over normal halogens, you're already jumping up over 2000 lumens or more and it makes a huge difference. That's $50 vs. $160 for the 55 watt kit. A lot of it has to do with the housing too. On youtube, they have comparisons but most of them have the 35 watt kit in the fog lights, meaning smaller housing, lower level of the light itself. I would like to see two Marks side by side, one with a 35 and one with a 55 and really see what the difference is. I'm sure the 55 watt is brighter but I can assure you that with the 35 watt kit, I'm not missing anything and I'm also drawing less power from an already power hungry car.