Well, I think proper font scaling would do wonders for making HN more accessible. As things stand, I have to zoom to 120% to read the text. I recall WebKit making a special case in its font rendering logic just for HN.
I can't speak to the font sizing. If I could change anything, I'd replace the table design with a plain ordered-list (ol). Simply because it is the proper semantic tag, and reading the table is unnecessarily verbose with modern browsers and a screen reader. Somehow ironically, Lynx fails to render the table as a table, so the main page is still nicely readable with it.