It would be interesting to see some kind of data on this.
I have a mutual friend that does tours in Europe. This was his and his worker's sentiments as well. Talking with them we thought there may be a lot of self-filtering going on in his situation. He does historical tours and those seem to attract a less rowdy group.
I used to have pretty poor handwriting as well. It didn't help growing up in school when learning to write they would just have me trace letters, and never taught what actually makes handwriting legible. A few years back I started practicing calligraphy for fun and it helped out quite a bit. The basics that translate to everyday handwriting are:
1.Use your big muscles to write.(Move your shoulder/elbow, while keeping your wrist and fingers relatively stable.)
2.Make sure vertical lines are all on the same angle. Vertical parts of "l's","h's","T's" etc...
3.The round parts of letters are the same shape (For example the rounded parts of "o's","e's", and "c's" are all the same)