I haven't checked all of these games, but I do know that Wario: Master of Disguise was the last VC game released with RenderScale support, so the games that
most likely support RenderScale are the following Nintendo DS VC titles up to and including Wario: Master of Disguise:
- Big Brain Academy
- WarioWare: Touched
- Yoshi's Island DS
- Mario Kart DS
- New Super Mario Bros.
- Brain Age: Train Your Brain in Minutes a Day (aka Dr. Kawashima's Brain Training)
- Yoshi Touch & Go
- Mario & Luigi: Partners in Time
- Star Fox Command
- Kirby Squeak Squad
- DK: Jungle Climber
- Wario: Master of Disguise
If you're looking to use RenderScale, you should start by injecting into one of these titles.
Note: Fire Emblem: Shadow Dragon released six weeks
before Wario, but does not support RenderScale.
It's a bit ironic, but personally I mostly use the RenderScale option for 2D games, because it causes slowdown in most 3D games. Using it on 2D games doesn't look as striking (although it improves things like sprite scaling and rotation), but it makes them look a bit sharper even when using the bilinear filter, because you're basically working with a 2x prescale.