Add exploration content, especially accessible introductory exploration content to get people hooked.
Exploration has one big advantage over missions: if it goes south, you can just cut your losses. There's no unfinished mission you have to either complete or lose standings. I'd much rather go to lowsec for exploration than missions. Rewards need to be comparable to wormholes, since the danger is.
Exploration also has a disadvantage: you need prober, salvager, analyzer, and codebreaker to make the most of it. That means more skills, two ships (ideally two accounts), or one pretty funky ship. This is a barrier to entry, you could get T2 launchers on your mission raven while you're training all that stuff. A hefty injection of lower end combat sites, paying paying better than L2s and L3s, might get newbies to check it out. Some of those newbies would keep at it.