A few other folks have made some interesting story suggestions already, but I'll dive back in anyway.
MMK, here is the problem: Enterprise is set at a different time from the other modern Trek series, with a different setting and background to be explored, with different constraints, and so on. But instead of doing shows that arise from the show's premise, the producers seem to favor shows that could be done with very minimal changes on any other Trek series. It's the same thing that happened with Voyager.
Here's some of what I'd be thinking about if I were writing or producing Enterprise.
1. Cut back on the aliens. We're still fairly close to Earth, closer than TOS was, and they didn't encounter a new alien every week.
2. Explore the Earth colonies. Are they going to be part of the Federation once it gets going? Are they sovereign? Are they Earth national protectorates? Are they bold pioneers, ravagers and polluters, political or religious dissidents? Are they xenophobic about the alien races humanity is now encountering?
3. Explore Earth. What are people's attitudes there to Enterprise, space exploration, Vulcans, space colonies?
4. Explore Starfleet. Are more warp 5 starships under construction? As the fleet grows, will Enterprise's mission change?
5. Explore boomer culture. They're the real heroes, taking risks in space without Vulcan help and without fast and well-armed ships. It can't be hard to come up with more than one story about them. Are they agitating for warp 5 tech to be made available to civilians? Do they see Starfleet as a threat, an impediment, a protector? Are they starting their own colonies, building their own space stations?
6. GIVE TRAVIS MAYWEATHER SOMETHING TO DO! He's got more space experience than the rest of the regulars. There must be situations in which he could offer useful advice or a different perspective. He'd certainly be handy in more boomer stories.
7. Finish the Suliban/temporal cold war quickly. It's produced some good episodes, but, as with the X-Files and its mythology episodes, the importance of it all fades to insignificance when you go back to weeks of business as usual without even thinking about this threat to your existence.
8. Don't try to recreate the TOS Kirk-Spock-McCoy dynamic. Archer, T'Pol, and Tucker can't pull it off. Their characters just aren't as well defined, and the acting isn't as strong. Try to develop an ensemble feel. Bring in more regulars if necessary. (Bring back Ensign Elizabeth Cutler, for a start.)
In short, Enterprise needs to do stories that only Enterprise can do, just as DS9 did stories that only DS9 could do.