alex775 I agree; any train that you wouldn't bother to upgrade if you get it is a waste.
But even a wasted train can be dismantled. Sure, that's only a consolation prize, but it's definitely not nothing. In fact, if you're buying trains from far-enough-back regions, they're usually a better deal than you get from buying boxes.
Here's a concrete example (at level 130 or so, because that's when I happened to write the numbers down—a lot of these numbers do change as you level up, so that's important to specify). You need a German legendary, but any other Germany train is wasted and will be dismantled. Today's daily offers include a small box for 20 gems or a blue German container for 30 gems (I think that's what they cost at level 130?), and you want to spend 60 gems. So, do you take 3 small boxes, or 2 region containers? Here's the expected value for each:
- boxes: 257.4 common parts, 28.8 rare parts , 4.5 epic parts, 0.75 legendary parts
- containers: 200 common parts, 104 rare parts, 19.5 epic parts, 0.1 legendary trains
That 0.1 average legendary trains (a 9.75% chance of one legendary and an 0.25% chance of two) is worth a lot if you need a legendary in Germany, certainly a lot more than 0.75 legendary parts.
But even assuming you aren't going to get lucky, averaging 200 common, 104 rare, and 19.5 epic parts for 60 gems is almost always much better than 257.4 common, 28.8, and 4.5 epic. Not always—sometimes you're stuck on common parts to upgrade your epic or legendary trains—but usually. And it's a pretty big difference, too.
That consolation prize may not be the best possible use of gems, but if you really need the train, the region containers are already a very good use of gems, and the multiple consolation prizes you're virtually certain to get along the way are still not a bad use of gems, and add them together, and… you should buy the region containers.
Not like you have a choice, of course… And in practice, I probably wouldn't buy Germany containers at level 130, because that's probably the time you least need a German legendary. (If you made it through USA with your current Germany fleet, stick with it until timber starts to be a major constraint—by which point hopefully the region containers will be down to 20 gems instead of 30, not to mention that German upgrade costs will be so cheap compared to Russian or whatever that when you do finally get the train you'll raise it to 60/60 without even thinking…)