So it looks like Amazon is restocking new copies of Dragon Quest V for the DS. You should probably buy this - even though they're $40, per its original retail price, it quickly went out of print, and most online places were selling used copies in excess of $60. (Granted, it's always been $35 at Gamestop, but they are difficult to find and may not even have the case/manual, due to some new policies of keeping them off the store floor to make way for 3DS titles.) It is definitely worth grabbing - it's basically the game that convinced me the Dragon Quest series in general was pretty good, and I still feel it's the best of them, even though the series overall is a little too conservative for my tastes. (Check out the review for a bit of gushing and very slight spoilers for the few hours of the game, of which explanation is necessary to convey why it's so fantastic.) (And apologies for not grabbing any English pics of the DS version of V, or for the DS version of VI at all - I just got the latter one myself last week.)
The case of Dragon Quest V is interesting in relation to how it got to valuable so quickly. Square-Enix prepped up Dragon Quest IV to be a relatively big title, but it looks like they overshipped it and the title underperformed, so copies can still be easily found for $15 and under. As a result, they printed substantially fewer copies of Dragon Quest V, even though that particular entry has a far greater reputation. It must've under sold too, since Nintendo took over marketing and distribution for IX and VI, but now since IX has gained some popularity, more gamers are looking back for the titles they missed, and V has the best word of mouth.
I think a lot of bigger publishers underestimate the power of word of mouth for RPG titles. The type of folks who play RPGs are also usually the types to hang out in forums and converse with other like-minded folk, and have a good idea of what's good and what isn't. If a particular entry in a series is bad, unfortunately, it then suggests that there's no interest in the series at all, cancelling further localization plans. Sure, Front Mission 4 flopped, but that's because it wasn't very good, not because there wasn't interest in Front Mission 5. And what about Valkyria Chronicles 2? It probably also stumbled, not only due to its downgraded release on the PSP, but the general reaction (at least in English speaking territories) of it being substantially inferior, but will that doom the localization of Valkyria Chronicles 3, even though it's purported to be better?
At any rate, buy Dragon Quest V. Show that there's SOME type of interest portable RPGs. I'd rather be playing my games on a TV or computer monitor, but I'd also play them on a portable over not getting to play them in English at all. (And while it's not on sale, you should also get Radiant Historia on the case of it being pretty damn good.)