Since you own Astra i suggest buy Petrol because:
1. You will love its smoothness and power.
2. Its ideal to buy Petrol If you keep the vehicle idle for long time(continuous 4 weeks lets say) once a while.
3. You are not bothered about resale value.
4. FE you can expect between 7-12.
5. Black or Red look fantastic on Innova, put some custom stickers like what I did.
6. If you are buying V spec and changing alloys send me those 5 alloys, I will pay you 12,000/-

7. by the time you sell your Petrol Innova you get good resale value since 8 years downtheline cost of Petrol/Diesel would be almost same.
Regards,
Ravi.