First, welcome to FlyerTalk, fauxfive55.

It would have been better if you'd made your subject more specific by mentioning that you are apparently only interested in flights to one destination (Vietnam). That is very specific, and most FF/CC experts are not likely to have experience with that specifically.

The general FF expert opinion is: FF miles are great if you are flexible about destinations, not just about (though also about) dates, carriers (within an alliance), routing, etc. For a more common example, FF miles don't tend to work well for those who think they can use them to take a whole family to Hawaii over Christmas vacation.

FF miles are an "excess capacity" currency. Airlines don't give away seats unless they think they will go unsold. If you want to go where there is ilmited service, or where "everyone" wants to go, and then on top of that you want to go when "everyone else" wants to go (say, during the times that kids and their teachers are off from school), you're a lot less likely to find FF seats than if you select a new route (which not many people know about) to a new destination (for the airline you collect FF miles with) and then are fleixble about your booking.

They tend to work better for people who want to fly to different destinations, who can say "ok, I can't get an award to this place this year, let's go soeplace else this year where I can get an award, and then let's try booking 11 months out for next year or the year after to this place".

So can you book 11 months ahead if that is what it takes? Can you be totally flexible about dates, or are you trying to syncrhonize with partilcular events (either here or in Vietnam) which restrict your dates?

By the way, many airlines don't allow you to upgrade from anywhere near the lowest fare. A few (like AA) use co-pays instead (and allow you to upgrade from any fare). But if it's upgrades you're after, you have to figure out which ailries that you're considering they're even "affordable" to you at. And remember, you can never upgrade (except perhaps on "full cost" fares) on any airline's metal other than one you have FF miles on. So, for example, I'm pretty sure you cannot use Eva's FF miles to upgrade on Eva's partners, only on Eva itself. Thus you cannot use the flexibility of booking with different partners for upgrades, only for outright awards.

(Having said that, I knowing nothing about Eva, and little about any other Asian carriers. I did once fly a business class award LAX-HKG on CX booked with AA miles booked about 10 months out, and it was great. But other than that I've never yet been anywhere in Asia that AA doesn't fly its own planes.)