I think there are some other variables you might not be considering Laura.
As you know I have been to Costa Rica. Upon return I also felt better than when I departed. Although I also did not bring my Vest (used Acapella), I did not attribute this healthy state to the lack of Vest. Is it possible? Sure, change can often do a person good.
Here are some points to consider:
1) I bet you ate fruit every morning with breakfast (can you claim this same healthy habit at home?) Maybe you even ate better at all meals?
2) I didn't drink milk while in CR because it isn't pastorized there and at home I drink 2 gallons a week. Although I don't believe milk to be a mucus producer I sometimes wonder if humans are not meant to drink cow's milk. Are you a big milk drinker? Or maybe there was something else you regularly have in the US that you didn't in CR.
3) I don't recall you living by the beach. You were by ocean water for days. Breathing it 24 hours a day! It's like a constant HTS treatment

4) From you pictures you seemed quite active... do you remain this active at home?
5) Stress wreaks havac on the lungs. <a target=_blank class=ftalternatingbarlinklarge href="http://news.yahoo.com/s/nm/20060830/hl_nm/lungs_dc
">http://news.yahoo.com/s/nm/20060830/hl_nm/lungs_dc
</a>I'm willing to bet you reduced your stress level while on vacation. Consider how you accomplished this and bring it into your daily/weekly routine back at home.
...you get the idea.
5) Also, like others have said, the flutter and Acapella require more participation. If you are a "strap on and go" Vest person with no induced mucus production at regular intervals I would deduce that the other mechanisms would be more beneficial to you as well. Learn to use the Vest correctly.
A few tips I learned from Scarlett81 and others.
1) Make sure your vest comes all the way up to your collarbone.
2) Follow Dr. Warwicks suggestion of frequency/pressure
3) If you follow #2, you'll do 6 sessions of 5 min's. Break between each 5 min. session and huff cough and spit 5 times.
4) Start to find your normal volume of mucus you can produce. Your AM amount will likely be different than your PM amount. Aim each treatment to meet or exceed these volume goals.
5) Do 5-10 min. of Acapella after the Vest to assure all loose mucus is out. My doctor swears that the Vest doesn't clear it just loosens the mucus. Since most of us are upper lobe effected, loosening and not removing can cause problems since gravity will move this infected mucus to our previously uninfected lower lobes.