I know that this question has been addressed before, but I just want to
check that the situation remains the same with the current releases,
or if anybody has come up with a cheeky workaround/better solution.

I am looking for a relatively efficient way of finding out how much data
in size is stored by TSM for certain files or file types (ie. .mp3 .wav
.avi )

I can get a list of the files with

select ll_name,hl_name from backups where node_name='XXX' and
filespace_id=x and ll_name like'%.MP3%'

If I know what volumes the node/filespace resides on, I can get the file
size with

select node_name,filespace_name,file_name,file_size from contents where
volume_name='XXX'

Is the file size accurate or is it the size of the aggregate that the
file is contained within ? (They all seem a little too rounded for my
liking)

Also, this is not particularly easy in a non-colocated environment.

So,............ is listing the volumes that the node/filespace is stored
on and then selecting from the contents of this list of volumes the only
way.
And, even if this is scripted, is it accurate or is it just the size of
the aggregates.

Knowing that the GUI will list the filesize but it doesn't seem readily
available from SQL queries is truly a Friday afternoon annoyance.

Leigh