I believe the dusty bin (321 unit) is the one normally stabled at Watford for the St. Albans branch line service but due the Watford blockade/upgrade it has had to be stabled. No room at the inn at Bletchley or kings Heath (Northampton) so they sent it there.
I believe the work at Watford Is over with for a little while so no idea how long that unit will stay there now.
It's very common to see a DRS 57 there as it's a thunderbird, we sometimes stable the odd 92 but they come and go to Daventry, it's only when Daventry don't have room they come and sit there until Daventry want them back to form a service.
Colas stable a bit at rugby now and right now all the former MLV's can be seen in the carriage sidings.
There are also some flats in the North end of the siding, they were dumped there a good time ago and I believe it was DB Schenker that left them (I may be wrong on that!) but I wouldn't be surprised if they have rusted to the rail by now!!!. These aren't 'spottable' from the station itself but if your depart on a North bound train then look to your right (in direction of travel!) and just a few seconds after departing you will spot them.