Too many to count. Unfortunately we've never really kept most of our older systems when I was growing up, whenever we'd get something new they'd either get put away in storage or just abandoned in a box in the garage until we forgot they were there, and if I ever had extra money it'd usually go towards newer stuff than retro things. If I ever wanted to play any older titles or whatever I had to resort to emulation, so the actual number of how many I've finished is easily in the hundreds.
Nowadays, even though I usually have a good amount of extra money on hand, I still go with emulation simply because it ends up being a better, easier, cheaper, and quicker solution than buying up older games I want to play.