I used to think having sick and vacation from the same pool was nice, because I rarely got sick and therefore had more vacation. I also like that I don't have to feel guilty about calling in, or wonder if I'm "really sick enough" to stay home. Knowing that it comes off your vacation time definitely removes some of the stigma of taking a sick day. But it's a double-edged sword, and it definitely encourages people to work when they really shouldn't, and share their germs with everyone else, especially if they have a vacation coming in the near future.

To your plan (which I agree with), I would add strongly encouraging companies to allow employees who are functioning but probably contagious to work from home when possible. It's not really something that can be mandated, because it's not feasible for all companies, but I think it'd really help curtail the spread of disease. Even when people have plenty of sick time, if you've got the flu or a bad cold, you probably don't stay home the whole time you're coughing and sneezing your head off. Having the option to get paid if you're able to be productive, while keeping your germs to yourself, would be a very good thing.