We have limited resources at our library for any kind of donor development program. However, we would like to start putting donation opportunities into our newsletter. But we feel that they would respond to very different kinds of messages. It sounds like you've done some good work in preparation for implementing your individual giving campaign. If there was one user-group to concentrate your limited resources on, it would be your seniors.
Seniors spend significantly more on charitable giving than the average population.
These figures were both roughly three times those of their non-elderly counterparts. The statistics bear it out - seniors have a better understanding of charitable giving, give in higher amounts, and give more often. Create your newsletter messages to appeal to the mature adult crowd of over 55, and statistically speaking, you should have better than average success.