I went through the same thought process, I think. I currently have a 2013 ST3, it's full Stage 3 and is making respectable power. When the RS was announced, I was drooling and figured I'd immediately get one if I could. As it got closer to the first shipment of them, I started thinking I'd wait to see the initial reaction for owners to see what bugs and nitpicks people have with the cars. The RS turned out to be a good car but my hype sort of wore off so I stopped looking for one. A few weeks ago, a friend of a friend bought a RS for about $53k after dealer markups, tax, etc. He offered to let me drive it and of course I jumped into it. At the time, it had about 1600 miles so it was after the break in period. So from my experience:
Drivetrain-wise it pretty much tops the FoST in everything except fuel economy. Interior-wise, it's the exact same for the 2016 models aside from obvious embroidery and some extra functionality for the drivetrain. Exterior-wise, it's a beast looking car. I find it looks somewhere between a Evo X and a ST.
Anyway, is it worth it? It all depends on what you're using the car for. Me, personally, I do NOT go to the track AT ALL and I have no plans to do so. I also do not race aside from some occasional highway fun. Most importantly, I DD my FoST and I drive about 400-500 miles a week. In my case, I do not believe the extra power and better drivetrain will be worth the extra cost of an RS. A lot of RS owners will tell you that when not pushing the car, it does feel similar to a FoST. The biggest complaint I see is that the car rides very stiffly even in the normal driving modes. Both of those combined with the extra loss of fuel economy makes the FoST a better daily driver in my opinion. Like I said, it all depends on what you're doing with the car. Again, in my opinion, I believe you're wasting an RS' potential if you're not taking it to the track.
When it comes down to it, I decided to not spend the extra tens of thousands on a RS and I kept my ST. I do plan on spending a few extra thousand and going BT to bump the power up to ~400 WHP but again, I won't be going to the track. That will be mainly just for some street fun.