On paper, your situation clearly improves as you increase the antenna mounting elevation. The improvement is significantly greater than what you would gain from simply replacing the antenna, preamp and coax.
If I were in this situation, I'd be looking for ways to safely mount the antenna(s) at 60' AGL or higher.
A possible solution to consider would be a roof mounted guyed push-up mast. Example:
http://www.3starinc.com/rohn_h40_tel...enna_mast.html