Garages and trade buyers know that the Alfa will be harder to sell than the Renault, so buying the Alfa is a bigger risk. This means they won't pay as much for a 147 GTA as they would for a Clio V6. They will, however, retail the Alfa for similar money while they still can, because the whole reason for being in the trade is to make as much money as possible. /Nobody/ in the trade will pay above bottom book for a 147 GTA - not even the Alfa Specialists. They will pay above bottom book for a Clio V6 though, because they're rarer, more sought after and therefore easier to sell.
Private Alfa sellers are notoriously unrealistic when it comes to car values. Alfas still have the reputation with Joe Public of being unreliable, troublesome and difficult - deserved or not - yet the people who own them still think they're worth big money.
Any car is only worth what someone will pay for it.
You left the smiley out.