My experience (and that of most people) is that Requip is basically an inferior version of Mirapex in terms of side effects and efficacy.
So you've developed a tolerance to Mirapex? Don't give it up! Try a drug holiday. I was using 1.5mg of Mirapex daily, then weaned off of it for a week, and am back to only needing 0.25mg a day.
The question is how to do the drug holiday. I would not recommend using another dopamine agonist (like Requip) as a substitute. Your neurologist may have some ideas (benzodiazepines? Maybe a mild opiate like oxycodone for no more than a week.)
Don't give up on Mirapex!
Here is a just-published (Jan 2008) meta-analysis of all the Mirapex and Requip studies done so far: http://www.ncbi.nlm.nih.gov/pubmed/1...b med_RVDocSum
Summary: Mirapex is superior to Requip in terms of efficacy and fewer side effects.