Make some people beg for curing from your friendly clerics. Doesn't make sense magical plagues can be cured by non-magical means.
It makes just as much sense as your wounds regenerating with herbs, and I feel that this is simply a headache no one really wants to deal with on top of already annoying diseases / poisons. I could see increasing the DC on removal however, that way untrained healers can't get rid of them so swiftly. (This still promotes your idea of player interaction)
I think that it would be better to be harder too. Bestow Curse is around the same trouble to cast, it causes more issues and it's way more complicated to find a cure that isn't a cleric. Not to mention that someone will be drained XP for it.
Also, it would be great that diseases had an incubation period without making the victims roll the save. With that, it would be easier for infections to spread and it would make it harder to track the initial vector.
For those curious, I suggest reading this old thread on the subject: Make Diseases Curses and Cia. a Bigger Deal (//%22http://www.efupw.com/forums/showthread.php?t=88817%22)
Not all plagues are curable by salutory tonics. It stands to reason those that are curable through mundane means can be done so through them.