I had a Triaxis + Simulclass 2:90 running into my Trad 4x12 in stereo. If I stood back where the audience stands, the stereo effect vanished. I also noticed some acoustic bleed-through from one side to the other within the cabinet. The only setting where the stereo seemed advantageous past a few feet from the speaker cab was when I doubled the guitar with a slightly delayed and detuned effect in the second channel. Also consider that depending on how the stereo cab is wired (par. / series etc.) you may not have the ability to use your chosen power amps.
Otherwise, stereo is a nice to have feature, but probably not worth spending extra money, IMHO. Whether you like the sound of the cabinet is much more important. My 2 cents worth.