I recently got a MacBook 3.1 from a friend that had a bad hard drive and I replaced the stock hard drive with a Seagate 500 GB hard drive running 7200 RPM. I was a little surprised at how silent the new drive was as after starting it to format it and load the OS X on it I could not tell that it had spun up, it was virtually silent.
The other problem is that it need new RAM and I went and got 4 GB of RAM from Staples (the only place that had any) Once I got everything together I put it in and everything is working great.
Oh BTW this is my first posting and I have a hobby called collecting old MAC's and rebuilding them as I enjoy the challenge.
I'd say go for the 7200rpm. I don't even think I noticed anything different from a performance standpoint, but it was the difference of a few dollars even a year ago when I upped my Late 2006 model from the stock 80 GB 5400rpm HD to a 500 GB 7200rpm drive.
Things got really sluggish as of late, so within the past month I went from the stock 1 GB RAM to 4 GB RAM (3.3 recognized in OSX). That seems to have helped a bit. Now I just hope my laptop can last for another year or more to make the investment worth it and before I can hopefully upgrade it.