Your Evo has very low mileage and looks like it's in very good condition. You could probably get more for your Evo than 23k if you sold it privately. Evo's and STi's have fairly good residual value.
There is also some wiggle room, for negotiating, even though 23k is the internet price. Also, the 3 series you linked isn't really loaded. If you are looking for that, I'd try to fair trade for one that has at least the premium package and the lighting package.
I recently purchased a CPO 10' 328xi with the M-Sport package and I love the car. It is extremely refined for a smaller car and handles very well. I've never driven an Evo but I would imagine the feel is very different as others have stated. Take it for an extended test drive and see if you really want to trade up. The best way is to experience the car and decide for yourself.