Hmm, I thought your 2nd car was an e-bike?I admit the Prius is bigger and I should have chosen a bigger car to compare it with.
Be fair to Citroen though, they have been improving their reliability over recent years (they needed to!) though it is not relevant to the C1 / 107 / Aygo topic. I wouldn't pay more for the Aygo since the engine is identical (as is just about all the car). More importantly it is put together by the same workers on the same production line.
The Aygo, C1 and 107 use the same Toyota designed floorpan and running gear and are built in £1bn investment factory funded jointly by PSA and Toyota. The facility was designed and equipped by Toyota and can produce 300,000 cars a year. It is situated at Kolin in the Czech Republic which chosen because of its central European position for the supply of parts and because of the ample availability of less costly workers.
If you buy an Aygo then, you are paying much more for a badge. If you want an Aygo buy a C1 and then order a couple of badges from Toyota.
As for residuals just how much can a £5800 car lose in a few years? It may be a Citroen but it should still hold it's value well due to the low running costs and low insurance making it an excellent choice for a 2nd car / young persons car.
Good thing for PSA that Toyota runs the factory. I still reckon an Aygo will be worth more in the long run - memories of dodgy French electrics run deep.