I've seen a number of people go from a rocket to a Tbird and so far all were happy with the switch. One guy bought a Tbird, started thinking along the same lines as you and traded the Tbird for a rocket. 6 months later he sold the rocket and went back to a Tbird. I don't recall anyone going from a Tbird to a R3 other than him.
I'm not saying the R3 isn't a worthy upgrade, but it seems not to be so far for the majority. There are a ton of R3 owners who swear up and down they'd never ride anything else, so it's all about the individual. For me, i rode one and was impressed big time with the power. Problem is, that was the only thing i liked and decided to stay with my speedmaster because i liked it better. Then the Tbird came out and that was all she wrote. My issues with the R3 were purely subjective as far as the demo went, but another reason i decided against it was that in the 5 or 6 months i researched it i read a lot more posts regarding mechanical issues with them than all other triumphs put together. When i asked about some of them all the R3 guys just got angry at me for suggesting they are problematic to any degree more than normal for any bike. That didn't make much sense to me tho considering how much i had read at the 3 R3 forums i knew of regarding serious issues. The owners who had issues told me it's true, those who didn't told me i'm halucinating. Go figure !In any case, there have indeed been a lot of issues some of which have no doubt been rectified, tho not all have i believe. Do the research before you buy to be safe. I also considered maintenance (ease and cost) and MPG which are higher with the R3.