If you are going to upgrade,
then upgrade!
Never, ever waste money and time on 'small' improvements. This just leads to frustration and an accumulation of less than satisfactory gear that gets sold at a loss.
Few of the speakers mentioned are going to be substantially 'better' than the F206, although some might play slightly louder before they distort. I don't think you really upgrade the F206 much until you get to the F328Be within Revel's line.
The best advice for a speaker 'better' than the F206, as mentioned above, is to explore the large bass-driver horn speakers by JBL and JTR, for example. Although all these choices are >$10K new, you never know what shows up in the used market.