Reason to abandon yellow letters list?

[Brian Stieler]

I took the advice of the forums and dove right in to sending yellow letters. I have a list of ~500 absentee owners, and everyone has now received at least 1-2 mailings. At the beginning, I was using a handwriting font that looked kind of fake and I was printing them on regular yellow computer paper. They looked cheap, and my response rate reflected that. I received 6 calls out of 750 letters (only 1 with potential). 

I decided to the time to completely re-do my design and now have very authentic looking letters and handwritten envelopes. I'm proud of these ones.

My question is:

Can I continue mailing to the same list, or did my first letters ruin my credibility? Should I stay the course, or buy a new list?