I do most of my gaming on a Retroid, which can run a lot of PS2 games well, as well as obviously earlier games. I really liked the GBA Macross game - you got to level up ship stats after each stage to make it more durable, or your weapons stronger, and shit like that.
What other shmups have similar mechanics? Dont care if theyre horizontal or vertical. I already have Radiant Silvergun's Saturn port loaded on my device, so inb4 that one.
A bunch have currency acquisition which you use to get weapons, etc. It ends up beign RPG-ish since you're effectively investing in a build from ernemy-harvest resources. Games like Lords Of Thunder, Space Fantasy Zone, Magical Chase. Also a bunch of overhead walk-'n-shoots set in medieval fantasy lands that operate like vertical shmups with RPG-ish mechanics like Undead Line, Gain Ground, etc.
Ginga Force on 360/PC has a pretty extensive weapons shop/customization to get parts between stages.
Any specific older ones you like most? Again, gotta be on ps2 or earlier, since these are going on a handheld emulator
Lords Of Thunder and Magical Chase, probably. And Gain Ground has a PS2 remake with a great soundtrack.