Some good news.
Most people who use email marketing - and that includes email newsletters - say that it's getting more effective, as this chart from Marketing Sherpa shows.
Says Marketing Sherpa: In general, the effectiveness of email for marketing purposes is doing well. More than 3 times the percentage of marketers who said the effectiveness of the medium is decreasing said it is increasing. Despite the challenges that marketers have with email, their opinion of the medium is still quite strong. This attitude is one reason for the continuing shift in marketing budgets from other tactics to email.