Lightspeed,
I do see increased performance and speed in 12-Premium over 11.5-Home but, it also has a bigger memory footprint. Nuance and Microsoft both state that Ver 12 is Windows 8 compatible but, I am still on Win 7 and plan to stay there.
In general considering the cost of Dragon products the most "cost-effective" move is to upgrade once you are at least two or more versions back, unless you have a good reason to move up or don't mind tossing out the bucks for the latest version.
(1) Premium version allows you to upgrade/port your user profiles to the next version and the Home versions do not, or so they tell me.
(2) I was willing to take the chance that (a) I would be able to notice any real-world performance improvement and happy to say I did and (b) willing to take the risk that it would not funk-up or just flat not work with Hal or some other apps I use.
(3) Most importantly, I got a decent deal by being a previous owner and working for a college. Nuance sent me an email "offering" me the Premium-Bluetooth upgrade for around $60.00 as opposed to the "full retail" price of $110.00 and upwards.