If he fits the seat that he's in and it installs well in your vehicle and you find it easy to use properly, then there is nothing wrong with the seat he's in. I suspect that you have a Graco Cargo, but it could also be the Nautilus. They are both nice seats, though the Cargo doesn't make a good booster seat.
At 35lbs and 2yrs old already, I wouldn't stress about turning him rf'ing again. There are only 3 seats out there with limits higher than 35lbs anyways, so in most seats he would've already met the recommendation of "rf to the limits of the seat." (I'm counting the radian as 1 seat even if there are multiple models.)
Now if you decide that you do indeed want to replace the seat you have, and want to try him rf'ing, there's absolutely nothing wrong with that - you just don't have much in the way of choice since he's already 35lbs.
For your current situation though, provided the seat is a good fit etc, I don't see a reason to recommend replacing the seat unless you really want to. It's possible there's nothing wrong with your current set up at all and both the Graco seats are nice, safe, seats - no need to spend money to replace a perfectly good seat if you don't want to.