Wow, Farmingville is a nice place to live. I road the train to the very end of Long Island once, loved it.
How many years has this setup been up? You are between two salty bodies of water, double check connections, especially since you use a rotor. But for me I would do that second to last, along with lowering and/or realigning (you are using a rotor). The last thing I would do would be to swap out or add new antennas.
Also, even though you use a pre-amp go buy one of those $25 - $30 dollar 18 dB amps in the Walmart/Costco/KMart TV accessory department and amp before you split. That's what I had to do before I could get WKSO PBS (before I split the signal I didn't need an amp).
Remember, it's just a quick trip to the discounter and you can take it right back if it don't work, which it may not because your biggest problem may be (at least one of) your converter boxes. To check that borrow one of your friends newer 32" TVs, they are light to carry around, preferably a Sony or major brand. With the borrowed TV check signals both amplified and plain. Do you neighbors use antennas & get WCBS?
Also you said your Zinwell converter box never could pick up WCBS. That is very telling. The engineering the SW & HW guys put in to tuning and locking onto the strongest signal, even when there is noise, is very important.
I'm not telling you to go buy a new TV, but breaking your system into components and trouble-shooting the easiest to the most difficult.
See this explaination for the Sony brand of (TV) tuner:
http://www.avsforum.com/avs-vb/showthread.php?t=1110510
So if you ever get a channel on the Suncast tuner but not the Zinwell tuner again try switching them out. It sounds like the Suncast is better engineered than the Zinwell. But try the cheap amplifier you can buy & return easily and borrowing a smaller newer HD-TV.