Looks like between yourself and Sully Jeff, you have this nailed.
can't debate any of these things - everything suggested technically works, i think some of it comes down to practicallity.
for me, i like to keep it simple, i have enough things that are hard work without creating more of them!
keeping aggregates with same disk sizes and using multiple aggregates makes lots of logical sense for this setup, you're not getting penalised for lots of spare disks because your working along the lines of raid group sizes been shelf sizes.
so for me, keep it simple!
glad you're a fan of the podcast - think it's a great resource for tech folk, NetApp customers but also for non NetApp customers if you listen to some of the recent ones around strategic design for example, NetApp based, but easily adaptable.
great resource - here's a link to the return notice, but you'll find links to the soundcloud and itunes subscriptions for it.
and as you catch up... if you listen to Insight Berlin Day 4 - you'll get me podcast debut 🙂 (blatant self promotion there!)
http://community.netapp.com/t5/Tech-OnTap-Articles/NetApp-Podcast-Returns-with-More-Tech-More-Information-and-a-New-Voice/ta-p/109596
hope all this has helped.