Hi there!
Found here that the difference between types is nothing but size. Is situation still same as of y2014? In particular, is it big deal to require every string variable of PL/SQL anonymous block to be otPLSQLString and for every ordinary block to be otString?

The size is indeed the only difference. If you require more than 4000 bytes of character data to or from your PL/SQL Block, you need to use the otPLSQLString data type.

It seems to be not only difference We've found that otPLSQLString doesn't work with unicode symbols at all