It looks like you enjoy classic arcade and action games, and you've got most of the classic systems covered already. The only logical step from here is to get into Neo Geo.
It can be frighteningly expensive, but only buy one or two games per year and you'll be fine.
You have three paths to choose:
Neo Geo MVSThe original arcade cabinets with interchangeable cartridges. Most games are under $100. Nowadays you can find people who take the arcade motherboard and create a "consolized" version of the MVS, allowing you to play it on a TV like a normal system.
Neo Geo AESThe powerhouse system that Nintendo and Sega kids whispered about on the playgrounds back in the day. It's essentially the same hardware and software cartridges as the MVS version, just formatted like a home console. The most expensive video game system to collect for!
Neo Geo CDA cheaper option. The games are the same quality as the cartridge counterparts, sometimes with upgraded CD soundtracks. The downside is that it can have long loading times and not every Neo Geo game is available for it.