Reorganizing queues online

Dear Friends,

I want to reorganizing a Oracle QUEUE table. When I tried to re-org this table I am getting many locking blocking issues as this queue is runnign 24/7 basis. and getting this error

SQL> /
BEGIN
*
ERROR at line 1:
ORA-42008: error occurred while instantiating the redefinition
ORA-12034: materialized view log on
"ADMIN"."AQ$_CUSTOMQUEUE_H" younger than last refresh

=====================================================

then I tried shrinking the space and getting this error

ERROR at line 1:
ORA-10636: ROW MOVEMENT is not enabled


Question 1>> What would be the impact on performace if we would keep row movement enabled for the tables permanently.

Question 2>> Instead of rebuilding the indexes post table shrink can we use cascade option with table shrink space itself.

e.g. alter table admin.CUSTOMQUEUE shrink space cascade;

what would be the difference if we use cascade option?

Regards
Sumit