I would think the Navi and alloys are what make the car stand out along with service history. I have had a look at autotrader and there are not many astra j's with over 100k (less than 6 years old) and even fewer going for £5k or above and they are trade sellers. I really hope you get somewhere close to what you want but I would say that £4.5k is more realistic starting price for private sale and £4400 is fantastic from trade in. For example, there's a 2011 Astra 2.0cdti SRi (125k miles) with XP styling pack, 19" alloys and Navi unit going for £3.5k on autotrader right now.
I have to say though that yours looks pristine for it's age, I would be tempted though to add more photos with all the doors open and tailgate open, give people a chance to see her in all her glory.
I have to say though that yours looks pristine for it's age, I would be tempted though to add more photos with all the doors open and tailgate open, give people a chance to see her in all her glory.