I have the same MacBook 4,1 (2.4 GHz, 4 GB RAM) and I would definitely recommend upgrading. Of course, it does not support multitouch on the internal trackpad, but 90% of the time I keep it hooked to an external display and bought a Magic Trackpad, and it is wonderful.
However, due to the horrible X3100, graphics are not always 100% smooth, but it's more than tolerable. For example, the graphic effect of going from full screen and back can be a bit choppy, but that could possibly improve with dot releases (I doubt though, considering the GPU is weak and 3+ years old).
Regarding 64 bit operation, all of my applications run in 64 bit mode. Not sure why anyone would be having issues with that...
Overall, I would say this is quite an improvement over Snow Leopard and have thoroughly enjoyed Lion since the GM came out. It will be great once we get an update or two to iron out some very minor bugs here and there.
edit: I ran the same command in terminal that was mentioned earlier, and it says EFI64 on my machine as well.