We bought our house house 6 years ago and my parents offered us some cash towards it. When my mum had mentioned it to my dad he said he had planned to pay for our wedding (which we hadn;t expected) but as she pointed out, house prices were rapidly rising and we needed to get on the ladder. So they gave us a few bob and we paid for our own wedding 2 years later. But ours was only(!!!) €10k so we managed with a lot of saving.
We would give about €150 as a couple for most weddings, maybe up to €200 for very good friends but that's only 2 or 3 couples. My bro got married last year and we gave €200 plus I made the wedding cake, but they were very generous to us and they're worth their weight as babysitters. Half that for 1 person. And if I went to an afters I would bring a gift worth €30 - €50 depending on who, etc. If I didn't go and it was a good friend I'd still get a gift, on teh basis that if they eloped I'd still get them one, it's a congrats on getting married pressie, not a thanks for inviting me pressie.
As for weddings in Britain, my experience is that the avg gift there is less than here. A good friend go married in England a year and a half ago and I was quite surprised to see that our gift was far more expensive than any they received from their English 'good friends'. 4 of us went, me and hub as a couple and 2 others that didn't bring +1. We bought a gift worth about €300, with us paying half and the other 2 a quarter each.
Personally I think there's too much money spent on gifts, when you hit 30 you seem to have weddings every other week and it can be hard to afford them. It's awful that your first thought when someone announces an engagement is how are you going to afford it. As someone else said about covering your plate, if you can't afford it yourself, don't have such a big wedding.