I've heard both the RS1i and the RS2i, although not at the same time, so take these comparisons with a grain of salt. My impressions were that the RS1i is better than the RS2i, although they really do sound very similar. No surprise there.
Specifically, I thought the RS1i's bass was slightly better extended and slightly more present. The RS2i's bass is a bit more neutral, so depending on your preference you might like either one better. I like the RS1i bass.
The mids seemed generally of the same take and quality on both.
The highs of the RS1i I thought were quite a bit smoother sounding than the RS2i's, so I take the RS1i here as well.
From memory, I think the soundstage of the RS1i has quite a bit more depth than the RS2i's. This is probably due to the cup length of the RS1i. So depending on your preference, again, you might like either one better. I like the RS1i.
Hard to say whether it's $200 better though. I love the RS1i, but I honestly don't think it's worth its price tag. If it was a $400 headphone, I'd own it. But when the SR60i w/ L-Cush pads achieves 80% the sound quality at 15% the price (my impressions from A/Bing), I can't justify the RS1i's at the moment. I think I will own them eventually though ;)