Is there an iPad PDF Reader app that has autoscroll?
To date, I have found only one PDF reader that has Dropbox connectivity and has autoscroll(after a fashion.)

It is PDF Reader Pro iTunes Link. It is a universal app that works on both iPad and iPhone and ties to Box.net, Dropbox, Googledocs, and iDisk.  It has an "Autoflow" feature that allows timed jumps (from 5 to 100 seconds) of a preset number of pixels (20 to 400.)  I bought it at the low price of $0.99 and it performs, pretty much, as expected.  It has some basic annotation capabilities and "scans" documents using the camera in the iPad 2.  I have an original so I couldn't test that feature.

I haven't used it a lot as I like the annotative capabilities of iAnnotate, but the app is a good fall back if I need the autoflow feature.

For $0.99 it looks to be a solid reader that fits the requirements you laid out.