You really can't make rash judgments about a park's attendance based off of one or even several visits, even during days that are supposed to be crowded. After all, look at SDC this year: the days that people expect to be packed are relatively light, yet other days have been completely swamped.
As far as getting new coasters though, they actually really need to add in another just to make up for the loss of 3 in the past two years. I'm sure some of the GP think the park is crashing.