It turns out the bigger RC2 key import works with SIMPLEBLOB but not PLAINTEXTKEYBLOB, thus advapi32/crypt.c test failure. A bigger key import doesn't seem to work with other ciphers (I tried with _RC4 and AES).
v2 changes: - add tests for PLAINTEXTKEYBLOB import with bigger size to rsaenh; - factor out alloc_key() function and use that instead of new_key() in symmetric_key_import(). Now this RC2 specifics logic is gathered in symmetric_key_import() where it seems to belong except for CPEncrypt() part which still seems to require a special case check.