After trying desperately to search for an answer to this seemingly well-known problem, I stumbled upon the solution late last night. If you're unfamiliar, the problem is to do with changing the baud-rate which Sparkfun's SerLCD (mine is version 2.5) operates. Keeping this short, your mileage may vary, but for me the solution is: wait until the splash screen is gone before sending the baud-changing command. It's undocumented, and I haven't tried disabling the splash screen yet, but that worked like a charm for me. Suddenly I can use any baud rate I desire.
(edit) to be clear, I'm talking like 5 full seconds of waiting before sending the baud-change command.