Read Oracle BLOB type via SQL

Probably not

The view that may display native stored compiled indexes is CTX_INDEX_VALUES Or CTX_USER_INDEX_VALUES (depending on permissions and querying user). However, given that the index value length is only 500 characters, it is unlikely that it is stored there. (Just start selecting randomly from those indexes, if it exists, it will likely be there.)

Looking at the view design, however, it is unlikely that those virtual XML elements are stored, as it's much easier to compile them on the fly and then load them into memory.

Alternatively, CTX_DOC has a number of markup functions, but none indicate the ability to access native XML.

You may also want to explore the discussion around metalink: 122255.1 (Unfortunately, I don't currently have metalink access).

It may be easier to write your own parser-to-XML (as oracle has quite a few excellent native XML functions) than try to hack around the full text index.

Gaius is right, use DBA_TABLES for NUM_ROWS and DBA_SEGMENTS for size:

select owner,table_name,num_rows,last_analyzed from dba_tables;

The num_rows count is as of LAST_ANALYZED date, which should be close enough even without running DBMS_STATS.

For sizing:

select owner,segment_type,sum(bytes)/1024/1024 size_mb
from dba_segments
group by owner,segment_type;

or (depending what level of details you need):

select owner,segment_name,sum(bytes)/1024/1024 size_mb
from dba_segments
group by owner,segment_name;

For LOBs you'll need to join it to DBA_LOBS, for indexes to DBA_INDEXES, for tables to DBA_TABLES. A lot will depend on your specific requirement. Since you mentioned you are trying to figure out used space in tablespace it might be as simple as:

select sum(bytes)/1024/1024 size_mb
from dba_segments
where tablespace_name='YOUR_TBLSP_NAME';

Your solution would really work only with small DB as it would not be feasible to read all data on large DB.

I am hesitant to post how to address ORA-1555 as in this case this it NOT your primary issue but just for completeness - you are on 10g using automatic undo management so your DBA would have to increase undo_retention in your database (the ixora link is relevant to a DB without auto undo management).