I'm in a similar position to Summerdays (or will be!) in that I will have a family of 5. However, at the moment the kids are small (one is still to be born) and I am looking to buy something that will do us in the future as well as just now. So as the kids grow and if the bikes get too heavy I could get a roof rack as well.
The more I think about this, the more I realise how expensive this is going to get in the future! I need a better paying job!