I think that's a common theme all around - that people who really care will be there with full enthusiasm; and while it will be sad that others can't make it for one reason or another, I've decided that the bonus will be that we get to have a more intimate wedding without too much craziness. I'm in the same boat as you - my honey's family is from the East Coast and my family is from California, and considering there are more from my family needing to attend, it made more sense to do it in Mexico (ironically airfare turns out to be pretty close regardless of which side of the country people are flying in from). And like you, I wanted people to make it a true vacation instead of just popping in and out for a wedding. Everyone's pretty much on board now, but I did get a lot of questions. The questions however came mostly from family members (older family members and relatives). My friends on the other hand were thrilled. I still hear my mother-in-law muttering about why we decided to do it in Mexico but I'm blocking it out because I know that once she gets there, she will love it.
I think the most important thing is to stick to your guns about why you're doing a DW and not take it personally when your guest list starts shrinking. That's what I've learned. And then just have a blast when the time comes, which for me will be in less than a month!
I've actually been kind of surprised at the amount of defending that I have to do regarding the DW. No one seems to understand that since my FH is from western Canada and I'm from NJ, one family will have to travel no matter what. I had a friend try to convince me not to have a DW, disregarding the fact that whether we had it in NYC or Mexico, my FH's family would have to travel no matter what. So it would still be a DW for them (and they will be at least half the wedding).
We chose a DW in Mexico so if people had to travel, they could make it a true vacation. Plus our families barely know each other, so this would be a great way to get everyone together for more than just a day or two.
Bottom line- the people we really care about will be there with full enthusiasm. The only downside is that will also miss some great friends too ;(