My 2 cents -
1. Relative graphs on dashboard - A graph with delivery statistics (open/click/bounce etc) for 3 months and one with subscriber details (growth,bounces,unsubscribes etc) for 3 months. If you want to make it complex, go for a pie diagram depicting % of types of devices used by the subscribers to respond to the emails and another one for showing campaign responses by geography. So total 4 graphs.
2. If you're looking at customers with basic knowledge, rename campaigns as "Compose" and Lists as "Contacts" on left menu. Under "Compose", give 4 sub menus compose a regular campaign, compose an auto responder, Groups and global custom/dynamic tags (You may include the last two options under some other menu). Under contacts, All contacts/subscribers, Contact/Subscriber lists, tools and "Suppression list". On the tools page, you can put that "Toggle filter form" option with a different name like "Filters". Because "Toggle filter forms" may go unnoticed in the present design and the name makes a complex sense to me.
3. There should be a new left menu item - Statistics. On the statistics page, list all campaigns with more fields - bounces, clicks, opens, abuse reports, etc etc. This is very helpful in comparing the campaigns. Also, there should be an option to export basic stats of all campaigns. When clocked on a single campaign, replace all the graphs there with a single relative graph, with sent, bounce, opens etc. Also you can include a pie chart for user agents.
#2 is from my experience. Replacing some terms with something that basic customers used to is a good idea for sure.
Add/remove based on your logic and expert advises
