The thing is, what most people would consider an exaggeration on their contents is probably more realistic than they think. So yes, I think you would be better off almost over-insuring, 'cause then at least you would guarantee replacement value for your belongings.

We usually don't realise just how much it would cost us to go out and buy new things for what we have.

The thing is, an assessor who comes out and values your goods (once they've been lost/damaged) does it every day and they will apply what they consider market value. If you aren't used to valuing, then your estimate is less likely to be correct. Just because you bought your fridge for $1K, for eg, on sale and got a discount two years ago, doesn't mean that the value of it should go down as $1K! To go and buy the equivalent fridge not on sale as soon as yours is gone might cost a lot more.

Use the online insurance estimators/calculators. Don't leave anything out.