San Diego's weather can't be beat !
A top notch RR museum with great clubs operating their layouts. However the property values have gone crazy, taxes are going out of sight and the state politics are terrible. But when your friends and family are here it makes it all worth while !
This is true of almost any place in CA. San Diego is especially wonderful. I live in the SF Bay Area but I prefer San Diego. Another downside to CA is the possibility of earthquakes.
The upside to CA is friendly people, fabulous weather most of the year (neither too hot or cold), lots of recreation, many museums, opera, special events and activities, good transportation, great medical centers, etc. The reason property values are going out of site is that so many people want to live and work in CA. This is the center of innovation and the high tech world.
As for model railroaders, all the major cities have large clubs, a few hobby shops, and there are more model railroad activities every weekend than anyone can possibly do. I could participate in some model railroad club, NMRA, garden railroad, museum, actual train ride, live steam gathering, etc., nearly every day of the week. The SF Bay Area TCA and NMRA divisions and the Bay Area garden railroad group are very active with lots of events.
The CA State Railroad Museum in Sacramento is probably the best railroad museum in the country. It has an annex at Jamestown, CA that restores and runs old steam engines and excursion trains. The shop tour is awesome. Jamestown is an authentic old west town in the gold country and is fun to visit.
For people who are into chasing real trains, CA has Donner Pass, Cajon Pass, the Feather River Canyon, and the Tehachapi Loop just to name a few places. This is real mountain railroading with spectacular views and frequent heavy trains. The nearby old west and gold towns are also fun to visit. Most towns have local museums that outline their history.
NH Joe