Upgrading from T1i to T4i?
Is it worth the $630 (or less) to upgrade?
I don't do a lot of video, so others will have to chip in there (esp regarding audio). When I do shoot video, I focus manually (the 18-55 motor is loud as you know). I don't have the 18-135 STM... (yet).
Will still image quality improve?
Yes, the noise and IQ will both improve. I had a 50D (same 15MP sensor as your T1i), and the new 18MP sensors are definitely better. The 650D's AF (and framerate) is also much improved over the T1i (My keeper percentage with the T4i is even higher than my 50D, which was no slouch in the AF department). I can only describe this camera as awesome!
Here are some of my first impressions...
And some samples in my gallery (click on "original" for best view)...
I am going to keep my 55-250mm and 50mm lenses
but lose the 18-55mm kit.
Sell it with your T1i? Good move.
Is the 18-135mm lens superior in all aspects to the 18-55mm kit lens?
Everything I've heard and from the reviews I've seen, the 18-135 STM will perform at least as well as the 18-55 in all areas. And of course outperform it in a couple.
I think the upgrade is a good move. Best of luck,
Good judgment comes from experience.
Experience comes from bad judgment.