I would think boiling more than the 60 recommended minutes would change things. How much, I don't know. I don't have much experience with that. I would think boiling the hops longer would lead to more bitterness and less flavor. I read this before starting and only steep in about a gallon of water, although I think that is still more than recommended.
5. Got Grains?
In order to get the colors and flavors you want from your specialty grains, without extracting excess tannins, you need to do one of two things — either steep in a small amount of water or in weak wort. A small amount of water means 1–3 qts. of water per pound of grains (2.1–6.3 L/kg). If you steep in a larger volume than that, add malt extract until the specific gravity is over 1.010 before adding the grains. And finally, rinse with a very small amount of water — 0.5–1 qts. of water per pound of grain steeped (1–2 L/kg) works well (see “Steeping,” in the May–June 2005 issue of BYO for more on this topic).
To be honest, the only problem I would have with the Midwest kits is the instructions. They are pretty generic. They have the same basic instructions for every single beer no matter the gravity. Of course if you read anything at all about brewing you should have enough knowledge that it shouldn't be an issue.