I have now visited all four properties listed above. This will be a combined review since the two Alofts and the two Elements are virtually carbon copies of one another.
The very first Aloft and Element Hotels in the country were the two that opened in tandem in Lexington, MA in 2008. They face one another and share a common parking lot. The Aloft and Element hotels in Boston also opened in tandem, just three weeks apart, in 2016. The Aloft hotels are modern, bright, and airy hotel with rooms that tend to be on the small side, but quite functional. The rooms feature platform style beds. The lobby has a grab and go style food service known as Re:Fuel. In fact, they will rolling out new grab and go food options during the course of this year. The lobby also features a very nice bar and lounge area called the W XYZ bar.
In contrast, the Element hotels do not have a lobby bar/lounge, but do offer a free buffet breakfast in the morning in the lobby. They also have a happy hour in the evening usually with beer, wine and some munchies. Clearly when the Element brand was created by Starwood it was their answer to Marriott's Residence Inn. The Element caters to extended stays with the rooms designed with kitchens/kitchenettes. The guest rooms also feature "Westin's Heavenly Beds" which are very comfortable.
The Aloft and Element hotels in Lexington, MA are conveniently located right off the highway on Route 95, whereas the Aloft and Element in Boston are located on D Street just a three block walk to the Boston Convention Center. Another great convenience to the Boston hotels is that they are only 10 easy minutes to Logan airport. This is the same Boston neighborhood that also features a Renaissance hotel and the Westin which is adjoining the Convention Center.
Based on what I have experienced, it would seem to me that these brands are here to stay and will continue to expand in the years to come.