One gotcha is weather. Depending on what you mean by spring, you could be rainy much of the time. The coast north from SF will be wet until sometime in June. South is beter.
Also, you say 500 miles - that is about what SF to LA is, so you might do that. Keep in mind that trains are not as good in the US as the UK, so you may be better off flying from LAX to SFO return. So, if you kind find a way to rent, ride from SF to LA, fly the bikes bake and return them. Then go on to Reno, which is straight east from SF.
I haven't riden that route, but I have driven it (a couple times). The part closest to LA isn't as exciting (in my mind), but Big Sur is gorgeous. I will note though - there are hills - This coastline is right along the San Andreas Fault. Other attractions - Hearst San Simeon "castle". The huge mansion built by Randolf Hearst, the New Paper millionaire, Monterey... Not a bad ride by any means.
Does that help?