Spark is 64 bit compatible since version 1.0.
Here is a little summary of the supported platforms:
Mac OS: VST 2 (32/64 bits), Audio Unit (32/64 bits), RTAS (32 bits), standalone (32/64 bits).
Windows: VST 2 (32/64 bits), RTAS (32 bits), standalone (32 bits).
We do not provide the 64 bit windows standalone because we do not think it is necessary.