My UI is scheduled for inclusion into the mainline client eventually. I'm just not sure when. This is why this thread is called "future bitcoin client GUI". Only if you want a sneak peak, you need to build it yourself for now.
But for that reason it's indeed a waste of time to implement usability features in the mainline client. So if I discouraged you in doing that, that's exactly the point

So that you can direct your development efforts to some place they make sense...
Ah okay - I didn't realise that the long term goal was to include bitcoin-qt into the mainline client - with that information it certainly makes sense to concentrate UI improvements on bitcoin-qt while still ensuring core features are placed into the mainline core. If I have any ideas for new UI stuff, I'll fork your git and work from there!
Perhaps it would be worth putting stable bitcoin-qt release binaries on the bitcoin.org website?
Will