Can a laptop hard drive's rotation speed have an affect on graphics?

You'll see better performance on everything. Faster spinning allows for faster data reads, which means information gets into memory and to the processor faster. It's got nothing to do with graphics, specifically.

Not directly, however if your OS is using virtual memory a lot (that is, you don't have enough RAM to run all of your programs and data at once) then the OS has to swap data on and off the hard drive all the time. Faster hard drive = less interruptions when the swap files are used.

Also, your new hard drive is faster because the files aren't fragmented (yet) on it, and because it is presumably a larger drive than the original

Hard drives write data from the outside of the platter in, and when the drive is getting full, it is writing on the innermost tracks. The inner tracks are way slower than the outer ones (up to 50% slower). So if you have 35 GB of data on a 40 GB drive, you are suffering badly. But take that same 35 GB of data on a 160 GB drive, and you aren't even 1/4 of the way into the drive, so the performance will be much better.

Logical result