As I've posted previously, weekend service north of Baltimore will not happen for the foreseeable future. (i.e., ever) Cecil County is the last truly rural county along the Northest corridor; even if its residents were of the mind to utilize such a service, and they are not, you'd barely have enough volume to justify it. It's 3.5X less population than, say, Mercer County, NJ, which is the probably one of the more sparsely populated counties served by NJ Transit. Harford County may have a Wegmans* and some slightly fancier McMansion developments and horse farms, but for all intents and purposes it's very similar. Frankly we are lucky to have what we have during the week. It is good that they made one of the return evening runs a revenue trip, because years ago I had several times been railfanning at Perryville in the evening and have some yokel show up and ask "I can take this train to Baltimore, right", and I'd had to explain to them they could only do so in the morning. Now, you could make a case that having the weekend service terminate at Martin State would bring in some passengers. That I could buy to a greater degree, but I think for quite a few of those people it will be just as convenient on the weekend (vs. the week since there is less traffic going to Baltimore) to drive to Balto. Penn. In other words they already live in a place like Towson and just use Martin State because it's easier to commute to in traffic than going to downtown Baltimore.
As for the Baltimore-Washington segment, it's positively insane it took this long. Surely the PRR must have had Baltimore to DC weekend shuttle type services at some point before bankruptcy and Amtrakification? It will take a while for a market to build, but I can't imagine the hipsters of either city won't take to it like a, well, insert substrate and desired thing of your choice here. Also will be of benefit to tourists; but again it takes a while to build these markets. I still encounter people commuting to BWI on the MARC train who have "lived in DC for 4 years" and "just found out" there's a train they can take to an airport other than National.
* which btw is a terrible Wegmans compared to the nearby ones, even the one in Cockeysville. They don't even bother to carry organic apples anymore because nobody was buying them besides me, apparently.