Yes, as you have wired only one 'speaker out of phase, you won't get any stereo effect, i.e. you won't form sharp phantom images between the 'speakers. Also, low bass will cancel, so you'll get more perceived mid and top.
As to 'room filling', again, as there's no sharp central image, what you have is diffuse and could be called 'room filling'. As to a wider stereo spread, really there isn't a stereo spread as stereo (i.e. the creation of a phantom image between the 'speakers) requires both 'speakers to be in phase, as that's how stereo works on our bra
If you want to try 'room filling', you could put both 'speakers back to the correct phase, but turn them to the wall, so all the sound gets reflected into the room, especially if the 'speakers are angled to the wall rather than square. You may recall the Bose 901 'speakers which directed 89% of the sound onto the back wall and only 11% forwards which gave a very diffuse stereo image, the 11% in front just enough to give some localisation.
As stereo is a 'trick' played on our brains which interpret the two sounds from the loudspeakers to create phantom images, you can change the presentation very easily by 'speaker placement. As to the out-of-phase operation you've experienced, I don't see a particular value to that given that bass will cancel. At low frequencies where the wavelength of the sound is larger than the room dimensions or spacing between loudspeakers, as one loudspeaker 'sucks' when the other 'blows', the air pressure variations will cancel, so eliminating bass energy. This won't happen so much at mid or high frequencies where the wavelengths are much shorter.
If you want to research this further, look into how stereo works on the mind.
S.
