Well lets not forget the name of the tool, SQL *Developer*. First and foremost, it is a tool about providing facilities for developers. That there are some features for DBA's is a bonus rather than the guarantee :-)
In the time you typed your review, you could have searched our site instead and come up with this piece of code:
select dbms_metadata.get_ddl ('USER', username)
from dba_users d
UNION ALL
select (case
when ((select count(*)
from dba_ts_quotas
where username = d.username) > 0)
then dbms_metadata.get_granted_ddl( 'TABLESPACE_QUOTA', username)
else to_clob (' -- Note: No TS Quotas found!')
end ) from dba_users d
UNION ALL
select (case
when ((select count(*)
from dba_role_privs
where grantee = d.username) > 0)
then dbms_metadata.get_granted_ddl ('ROLE_GRANT', username)
else to_clob (' -- Note: No granted Roles found!')
end ) from dba_users d
UNION ALL
select (case
when ((select count(*)
from dba_sys_privs
where grantee = d.username) > 0)
then dbms_metadata.get_granted_ddl ('SYSTEM_GRANT', username)
else to_clob (' -- Note: No System Privileges found!')
end ) from dba_users d
UNION ALL
select (case
when ((select count(*)
from dba_tab_privs
where grantee = d.username) > 0)
then dbms_metadata.get_granted_ddl ('OBJECT_GRANT', username)
else to_clob (' -- Note: No Object Privileges found!')
end ) from dba_users d
Save that as a script, run it in SQL Developer (or Toad or SQLPlus or whatever) and there you go ....