Here is a screen grab of the the Marc Penn line southbound schedule.

Note train 415, departing Baltimore Penn at 7:00 (I get on at West Baltimore, so in my mind it's the 7:07 train). Also note train 517—my 7:23, and the times they both arrive at Washington Union Station.

Is it ever worth taking the 7:07?

Well, actually, yes. Because:

• Most commuters look at the schedule and make the same conclusion that you probably did: waking up at least 16 minutes earlier in the morning is not worth the 7 minute lead time you get in DC.
• With that in mind, even if they leave early they don't really rush to the 7:07; therefore significantly fewer people need to get in at each stop compared to the 7:23 and it usually gets to Union slightly ahead of time.
• Because of more people waiting on the 7:23 it tends to limp along in the last few stops and doesn't get to Union until 8:15 in the best of days.
• The 15-20 minute difference does mean a lot if you have to use DC's abysmal metro which gets crowded by the minute between 8 and 9.

These are the sorts of things you think about when your commute is almost two hours each way. If you would like to read more about extreme commuting (and who wouldn't?), this old New Yorker article is a good place to start.