Doubt it will hold its money any better once people understand it is the same car, on top of that, the C1 will have to lose an awful lot more of a percentage when compared with the Aygo.
Engines/Trims Year O.T.R. Price Parker's Target Price 3 Year Value
1.0 VVT-i 3d 05 £6745 £6600 £2755
1.0i Vibe 3d 05 £6595 £6450 £2461
Is what parkers states, although I am more than aware that the purchase difference is slightly higher. The important numbers there are the target 3 year values, as you can see, the difference is likely to be less than £300 (i suspect less since they are the same car and people will learn that). So if the aygo costs more than £300 higher, forget it.
If however image is all important to you, firstly you should gain maturity and then buy the one that makes better sense, after all, it is the same car.
As has been mentioned however, there are numerous better purchases out there, especially for a young new driver.