Disk RAID/mirroring/hot spares, etc

Don't laugh at how naive I am in this.

We have an i5 520 at V6R1, 16 35gb drives, RAIDed in 2 sets of 8.
They are on separate controllers (for sure) and separate buses (I
think). Two 3581 LTO-2 tape drives.

After a great presentation at our LUG the other morning on clearing up
disk space (Thanks, Rob Berendt) I found and removed 146gb of old
performance data from V5R4 that was created when I moved to V6R1.
Coupled with removal of an IXS card last summer, we went from 45% disk
utilization this morning to a current disk utilization if 15%. That's
a lot of room and I came up with some ideas.

1) Could I take 1 drive in each set and make it a hot spare? Each
RAID set would then have 7 drives and I would have 2 hot spares.

2) Virtual tape. Backup to virtual tape, then DUPTAP to physical tape
to lessen the backup window. What I read on virtual tape, though,
leads me to believe it won't be much faster than direct backup to the
physical tape drive, if at all.

3) Here's the one to laugh at. Could I split these disk drives into
separate ASPs (or whatever they would be called) and have one of them
be a mirrored backup of the other? The OS would keep them in sync,
and when I want to do backup, tell it to suspend this mirror, backup
the second ASP onto physical tape, and then resync the mirror?
Therefore there would be no backup window whatsoever, and the tape
backup I created would be identical to what I'm doing now? Including
the SAVSYS done every week? Am I off my rocker here?

Thanks.