DS was a much better system for RPGs, so you should find a way to get these games for an attractive price somehow.
Otherwise, for the console itself, there are some pretty good RPGs as well, even if Atlus really was in a era of recycling stuff and did not do many brand new games. They even totally neglected the 3D effect in later games.
Radiant Historia Perfect Chronology : good game, even though I prefer the original one as the added content is unnecessary.
SMT Strange Journey Redux : haven't played it yet, but the original on DS is my favorite SMT game. I fear that it might be the same case as Radiant Historia, with useless new content. No 3D effect as well ! What a wasted opportunity !
SMT IV : very solid entry in the series, should definitely play it.
SMT IV Apocalypse : haven't played yet. Should be bought on eShop for decent price.
SMT Soul Hackers : did not age well, would avoid.
7th Dragon : haven't played, but it was on my radar.
Fire Emblem games : there were quite a few of those, I don't like the series much, but having only played Awakening to some extent, I can say that it was top quality. Echoes is a remaster from an older game, if I am correct.
Devil Survivor : I think Atlus made two remakes of the DS games.
Etrian Odyssey Untold : again, two remakes from Atlus with a new storyline.
Etrian Odyssey : there was at least a proper entry for the series
Etrian Mystery : I didn't like this mashup. I would have preferred to have Shiren 4 in the West...
Persona Q : there are two D-RPG with fan-service for the series, they look like they are pretty good quality
Overall, 3DS was a bit disappointing for RPGs, but it was a very nice step up for platformers, especially because of the 3D effect.
DS is where you can find a lot of RPG gems. Things like Hero Saga Laevatein, Knights in the Nightmare, Golden Sun etc...
I think that you are right to create a library of 3DS games now. This console marks the end of quality dedicated handheld experiences. I have a 3DS XL, entirely black, and it is a great console to play, big screen, games optimized for handheld etc... Quality experience, tailored for handheld gaming, with a lot of 2D gameplay (much better in my opinion than full 3D when playing with handheld ergonomics).
I really suggest to check a few other games, there are many great ones to play in 3D. Good luck !