Lisa,
This makes me recall a few special events with me and someone I thought was my close friend that ended up betraying me after I mentioned I didn't have as much energy to be on the phone for an hour or longer after my son was born - what was worse: she turned others in our circle of friends against me and then tried to get them to believe I did some 'stalker-type' thing to her, when I was laid up in my home after a surgery and a new baby (My husband was livid and actually took - and emailed - photos of my brakes to show the car wasn't moved in weeks as they were rusty.). She never cleared the air, even after we tried to reconcile... needless to say, I never trusted her or was truly comfortable around her again.
I also regretted sharing my special moments with her as they felt somewhat 'tainted' in a way. I went to her wedding before all of this, and she came in for the first ultrasound with my hubby for my son. She threw the shower (after much drama and stress between us over it and other things) and I still can't really look at those pictures. :(
I would say that if you are not close - then do not go. If it were me in your situation, I would send a decline. I feel in many cases, weddings especially, many want a huge turnout and yes, gifts are a great bonus as the couple will not have to purchase something they want to have.
If one does not go to a wedding, I really do not think you are obligated to purchase a gift. We don't. The way the economy it right now, I think a person cannot expect something from someone if they do not go - nor if they are that close. (Just my thoughts.)