1) What do you have?
Sega Turbo upright
2) Do you play it?
Yes.
3) do you regret getting it?
No. Most played (non-pin) at parties. (This could be due to difficulty...most people never make it past the first stage).
4) Would you rather have a pin in that spot?
Hard to say - I'm obsessed with pins right now, but I could buy 10 Turbos for the price of a pin.
Saw someone mentioned Crazy Taxi. Based on the number of times I played it on the Dreamcast, I can confidently say that I'll never get tired of it - though eventually you'll get to the point where a game lasts you 45 minutes...which isn't something you'll always be up for. That game in particular would probably be great replay value for you, as an owner, but would probably be less of a hit with guests who would probably get more out of Cruisin USA or Daytona.