I took my centre speaker over to two friends' who also believed a centre was not necessary, and after trying a few films with/without, they both bought a centre speaker and said it (watching a film), was a MUCH more involving experience with a more even soundstage where vocals were much better produced, and the whole film sound stage was more clearlly defined. And, as for the poster who doesn't use a pair or rears!!! Wake up man, you're missing a MASSIVE amount of film experience.
Trust me, I'd have no problems spending serious money on a center speaker.
https://www.crutchfield.com/shopsearch/center_channel_speaker.html?fa=1#&price=1370-3340
But as I just explained above, all DIY speaker builders I've consulted strongly advise not using dissimilar drivers in mains and center speakers. But are you saying from experience that YMMV that much in favor of disregarding this advice? I'd hate to have to ship a > 45lb center back to an online store.