More pleasing to the eyes and not from the 90s. A more attractive site wouldn't turn people off as soon as they visit it and would yield more users and support. Ubuntu's site for example looks nicer and only 0.1mb larger.
That's not how it works. I don't think the people on top of the debian community would just let anyone redesign their home page, even if the website would be objectively better in some regard.
Oh, there would be a debate, for sure. It will probably go through a lot of bikeshedding. But if you demonstrate competence and commitment and stroke the right egos, it can certainly happen.
I don't think a nice website would translate to that much more benefits, like new Debian users. If Debian was an online clothes retailer, and they wanted to compete with other such websites like asos.com, they'd need a website like them. But even then, Craigslist is also very popular, and the website design is similarly dated.