Your wedding, your choice.
I have been to weddings abroad (though they were all in a country that had a connection to either the bride/groom or a family member - they lived or had grown up there). I could only afford to go to those where we were provided with free accommodation. Or the cost was significantly reduced by those organising it.
I've never been for more than a weekend because I can't afford to take that much time off for weddings - and I have a large extended family which means there are always 3 or 4 to go each summer, by the time you add friends. That's a lot of holidays. The fact yours would be in the summer is an advantage, more likely to have time off - however, I doubt anyone would take a 12h+ flight for a 1 day event.
It really depends on the financial situation of your guests. You mention a £6000 trip to Nevada without it being a stretch - well, that's one year of rent and bills for me, so I couldn't afford it in a million years. 1k, best friend and holiday availability - I would think about it. Still no promises.
As long as you don't get upset when someone can't come, or when they make comments about it (I would HATE going to an all inclusive resort in Mexico, no matter how nice, it's my idea of a nightmare) - then I'd say go ahead. Only you know what audience you're catering this event for.
To sum it up, I'd personally attend a wedding abroad if my accommodation was covered (or very cheap), expenses throughout the weekend were covered, I had the liberty to take all my family with me if I needed, and the wedding was a £20 Ryanair flight away.
I travel enough for work as it is and for a family of 4, that trip to Mexico would be £4k unless I leave them all at home, which I would've already been doing all year round.