To be honest they way Impreza's are selling at the minute that is overpriced at even at 5.5k sorry to say but I recon your look at 5k if your lucky.
The money you have spent is spent and it realy doesn't affect the re-sale value.
Don't worry your not alone I payed 5.5k for an RB5 18 months ago and accoring to glasses guide it is only worth £2k
It realistically is worth 4 to the correct person though
That is why it is getting turned into RB500