If you promote, you will be playing teams with a larger fan base than your own, which will meant that you will probably have just as much attendance if not more than you do now even with a bad run. I've had a horrible season; got kicked out of the cup in the first round due to being matched up with another I.1 team, lost against my rival, performed badly on TV, had a major losing streak, and most fan surveys came in with the total average being 1.5~2 basketballs.
I've built up my arena AND increased ticket prices, and I'm still selling out, even though I'm playing like the Clippers. It helps to have teams with bigger fan bases and plenty of success coming to your arena :)