I'll be honest - I wonder how good of a use of funds it is ... I guess I am not sure what products Siemans makes that I might by and be like "hey, Siemans sponsors SEE so I am going to buy their product instead of another"
Siemans makes a ton of electrical components like controllers, sensors, relays, circuit breakers, etc. Even though they aren't the thing typical homeowners would go buy, they are used in thousands of different companies' products, so it is possible that those people would get a good feeling about Siemans at EPCOT. For example, the electrician that wired my house used a Siemens circuit break panel, there are at least five other brands he could have used some of them cheaper, but for whatever reason he picked the more expensive Siemens.
At a previous job I spec'ed out a lot of electrical control components, and bought a lot of Siemans stuff, as well as Allen Bradly and Honeywell. The biggest reason to pick one brand over the other is your experience with them, cost and your general feeling about them.
They also make one of the most popular CAD programs (UG NX), when someone is deciding between UG NX and SolidWorks, it may help if they feel like they "know" about Siemens when most people have probably never heard of Dassault Systemes.
Anyways, I bet the real reason for their sponsorship was what someone else said, they were bidding on a high speed rail project in the state and wanted to get their name out there. Probably the same reason they offered to redo the monorails, get people to think of them as THE train company.