Propably very easy to add:
I'd like to see a "spectate" button in the connections list (just like "kick" and "ban")

That would be useful in league-races and trainings. (where you'll never "ban" someone, but sometimes "spectate" in trainings)

It is there. Just press on players controller letter (e.g. W - wheel) and you'll be speccing him

Really? Didn't know that.

But it somehow doesn't work on our servers (running X12)

i think the OP meant that the particular racer is sent to spectate mode , not that you are viewing the particular racer.
The function to send someone to spectate modeis currently not there.

I have thought of that idea before - where you just force someone to spectate for the rest of the race, esp. if there just sitting there idling and blocking the race for another driver to enter.

If I understanded right - an option where we can vote for a person to go to spec mode?

If thats the thing, then it gets a +1 from me.
Can be usefull when someone desides to go eating while they let the car be on the track.

Actually I think the kick option should be replaced with an option to spectate. It would really make far more sense seeing as atm a kick doesn't stop the person rejoining.