I know it increases the content and thus the slot-machine surface area, but Show/Ask represent a good portion of my desire to come HN at all. There are many super interesting posts that never make it to the front page.
Another way to think about it is i often want to see discussions and projects from HN folks. The frontpage can often just be full of popular nonsense - Reddit-esque. However ShowHN and AskHN often have gems that are obscure, with a much smaller amount of points.
Yet another way to look at it is: i'd love a toggle filter to only show me AskHN/ShowHN on the front page. However most days it would only be one or two posts.
Hopefully this illustrates my desires :)
(one final example, hah, might be this very post. I suspect it'll get over 100, but currently it's sitting at 60 pts)