Importance of Center Channel in small room

I have a small room, 12x13. I use a center channel, mostly with three channel, hybrid SACD's. Most of the latter come from masters that were three channel mono. So, the hybrid is three mono channels. Miles/Blue is one of the disk's and and sounds great. I also use the center for other two channel stereo, using a VAS 1 preamp that has a center out.

You are right about the sound stage, I have the speakers, ProAc's 1sc, about a foot off the side walls.

Tweaking goes on.

Yes, even in a smaller room, the cc speaker does improve overall soundstage and imaging when it comes to playing music in surround sound or even 3 channel as for Tiger above. No question about it.

As I built my HT system over time (as funds allowed), the center channel was the last speaker I purchased. I was using the TV's speakers as the center channel for dialog and it wasn't bad. It worked. For music though, no good. I then went to small satellite type speaker for the center channel and that certainly improved the dialog for a while. Now I just recently upgraded to a full blown cc speaker (new B&W HTM61). Now the entire overall sound in music, movies, concert DVD's, and dialog has improved considerably. But that's the fun of it. Going one step at a time. For pure music, this HTM61 has greatly improved the soundstage, bass extension and punch, detail, vocals, and imaging of my system (Rotel A-V receiver). For movies, dialog is far superior now. So yes, it's important not only to have a cc speaker but the selection for your particular application is equally important.

Problems: with no center in your small (acoustically very difficut) room, you will have to sit smack dab in the middle of the room to get a Phantom center. If you don't, yo'll have dialogue collaps into one speaker - not connecting with your monitor/video immage. If you, on the otherhand, do sit in the middle of the room by yourself, you've now put yourself in a horrible acoustical spot in your room, yes! (that's where all the nasty peaks and dips in the frequency response is.)
In small 10 x 12'ish rooms, I'm alsmost always using two seat setup's, with the seats either in the 1/3 width and lenght dimmensions, or in the 1/3 width and 1/5th lenght dimmension (or, with smaller seats, maybe 2/5th and 3/5th width positions, depending).
These positions, in relation to proper speaker settings (in rectangular closed-in rooms), offer smoother frequency response, fundamentally.
So, if it were me, I'd give up on your center, so called, "sweet spot", and do dual seating arrangements - if it were me. And, I'd be DEFINITELY chosing a center speaker, yes.

Center channel is needed for off axis listening - especially far outside the sweetspot. If you sit in the sweetspot then you are actually better off without one of those horizontally mounted center channels under the screen.

Think about it - would you listen to stereo with one speaker turned upsside down => that is the equivalent effect of a center channel that sits two feet below the mains...it creates all kinds of problems...

As it has already been said, if you only watch alone and sit in the sweet spot, you can do without a center. If however, anyone joins you and sits to the right or left of you, as you keep the sweet spot to yourself, their experience, will not be as enjoyable as yours.