I have a 3DS and a Vita, and if I had to pick one to play forever it would be the Vita. It's just a shame that it doesn't get much love from Sony anymore. Not sure if you're a PS+ subscriber, but you should look into subscribing because you'll get at least 2 free games every month, plus they do a lot of really good deals as well. I just picked up the Tales of Hearts game for $5.99 last week, which is a great price.
There's some games you haven't mentioned that I think you'd like based on the games you talked about above.
Tales From Space - Mutant Blobs Attack. It was a digital launch game I believe, and it was definitely one of the best games to get early on. It's made by Drinkbox Studios, and I'll be listing some of their other games here as well. The reason I think you might like it is because it's a platformer kind of similar to Loco Roco. Charming from beginning to end.
Severed - Another Drinkbox Studios game. It's a first person dungeon crawler, where you you use the touch screen to swipe and sever enemy parts that you use to upgrade your character. Came out a few months ago, and was one of the best games I played in an already fantastic video game year.
Guacamelee - The second Drinkbox made game. It's a Metroid style game that has a visual style I find similar to Samurai Jack. You can get this on the 360 or PS3 as well. I know soon Drinkbox is coming out with a Drinkbox Collection soon for the Vita, so if you're interested (which you really should be, their games are great), that might be the cheapest way to get all of the games.
LittleBigPlanet - Some of the touch features make this game more enjoyable than the PS3/4 versions. I had fun from beginning to end.
Final Fantasy X/X-2 HD remaster - You seem to like RPG's, so I'm sure you've played this. Playing this on the Vita at work/school/toilet is awesome!
Killzone, Uncharted, Hot Shots Golf, Freedom Wars, Persona, and not to mention a vast collection of old PSP and PS1 games make the Vita an awesome system to own. I bought it for $250 when it released and I'm still happy with my decision, I just wish they'd make more games for the thing.