If you're comparing it to PSP, PSP's 3D hardware makes it easy to modify textures in real time so you can use it for scaling framebuffers. It can probably be done on Wiz too but there's no obvious software interface for it. It might be doable with OpenGL ES but it remains to be seen if there's a lot of overhead involved in binding the texture or not.
Picodrive is supposed to have a software width-only scaler, although a lot of Genesis games run at 320 width to begin with. If it doesn't have the feature then I'm sure when notaz updates it it will. Temper has this option too.