Let's look at the question in a more general way.

Where I live, £3 (~3.41€) won't buy a pint of beer in most places (and I don't want to go to most places where it does). Still, while being completely useless, I have no problem buying a few pints almost every weekend. And this seems to apply to a lot of people around here.

So definitely £3 is an amount that can be thrown at something without much consideration. Heck, I just bought a branded can of energy drink and a pack of cookies for about that amount from a grocery store. Good value?

Now, that will depend on what they do. I wouldn't pay for a fart app, or some bikini pictures. However, if something is useful (and I happen to need it) or fun and has a value for me, I have no problem of paying a few € to the developers for their good work.

Also, I will definitely pay 3€ for the AB level pack. It's one of the finest mobile games I've seen so far.

For me, the biggest question is how to determine the value before deciding to spend. I think that the model of free "trial" version with limited content works well at least for games.