When is literally impossible to find the game/system in my country (at a reasonable price) or if its a game I already own. With that said, emulation is not a bad thing even though if its a PS2/GCN/Wii game, because the person wasn't really interested to buy it in the first place.

Not that bad really, in the last 2 days Ive downloaded 100+ DS games for my R4 card =P

If you own the game it is perfectly legal to play it on an emulator provided you obtain the ROM/Iso from your own Cartridge/Disc. Most people will just download them though which is still illegal

If they're not really selling them anymore, I think it's fine. Generally, I'd say to generations behind the current one.

I know emulators itself are legal but I heard that using the propriatary software like the BIOS for example is illegal.

Same. It is an absolute last resort after exhausting all legal means.  If I do not have the money to afford a game, then I just do not own it.

Not really, you sound like a thief trying to justify his thieving. Pirating a product someone else made and sells for a price, is not economical, it's dickish. Economics doesn't teach us "when you want a product but can't pay for it, just take it anyway".

I've done it with three games, the first 3 Phoenix Wright games. I haven't done it since, and I won't either. It ain't right. If the game ain't worth my money, then it ain't worth pirating either.

Sweet! N64 cartridges are USB compatible, right?

When it is convenient to do so, I collect video games, have thousands of them for every generation around my house, I also have a pspgo, which is capable of having librarys of many of these old games on it, I could go and seek out the missing NES games from my collection on Ebay and pay some random person on the internet a few hundred euros to own them... would that money magically go to Capcom for the Megaman 4 I'm missing or Nintendo? No, nor would I be able to put that cart into my psp if I could get it.

While I know that some NES games are being trickled onto the Nintendo Eshop on the 3ds I am fully aware of it but in an ERA where MGS2/3 hd collection is on the psn store on my Vita for 8euros, seeing the whole 512kb that is Super Mario Brothers for the NES on the eshop for exactly the same price I would literally feel stupid if I were to pay that, and equally have no less a complete NES collection in my home.