You're right. Unless you have some predictable, ongoing medical expenses, putting aside money in an FSA is worse than gambling. I use all of mine every year because I see a provider who isn't covered under my insurance, but I don't think someone who's healthy should bother. If you have a physical and 2-3 routine doctor visits a year, it's not worth it.
The HSA is interesting in that the money you put into it does not go away. For those close to retiring, the funds stashed in one are still very usable after.
Something an FSA administrator will never tell you is that while you forfeit unspent funds at the end of the year (actually March of next year), you also don’t have to pay back funds if you quit/are fired and the amount you spent was more than your contributions to that point.
I recently quit my job in January. Spent the entire $2,700, waited for FSA reimbursement, then turned in my notice.
HSAs seem a little less problematic, but they still don't seem like a wonderful thing outside of certain circumstances.