Bella33,
I have a prescription for 200 mg Provigil and do exactly what you mention - I split the pill in half. I infrequently need to take it and do so on an as-needed basis. I take Requip XL regularly and periodically am not as alert as I would like to be - primarily if I have not slept well. On those occasions, and especially if I am going to have to sit in a meeting/conference/etc all day, I will take half of a 200 mg tablet of Provigil. It works.
I have not noticed any negative side effects other than if I take it late in the day, I tend to have trouble making myself go to bed/sleep. I do know folks who have taken it regularly and done fine with it.
Not all insurance plans will cover it. Since it is a med primarily related to sleep, some insurance companies don't consider it a PD med (because no one with PD has sleeping issues, right?). You might want to check with your insurance company to make sure they cover it - it's expensive.
lizzy4451