How important is the alcohol?

For a lot of people, the best part of a wedding is the open bar (sad, but true. Weddings can be super boring). The venue Mr. Spaniel and I are using includes a three-hour open beer and wine bar in the base price, but not a full bar. I had thought that the full bar was an extra $25 per person per hour, but I've just realized that I misread the prices, and we could do a signature drink for $15 per person for three hours. Which is awesome, because I would love to have a signature cocktail, which I think really adds to the party because (1) more people are drinking, (2) people have more fun when they are drinking, and (3) a signature cocktail can really help tie together a wedding theme.

Anyway, we're not totally sure we want to commit to the extra expense (it's kind of a lot, you know?), but if we do, I'm trying to think of some good signature cocktail options that would fit in our wedding. We're getting married on the first day of spring, and while our main wedding colors will be primarily black and white/ivory (at least in terms of what the VIPs are wearing), all of our accents will be in shades of green (flowers, fabrics, and anything else that isn't a dress or tux on someone's body!).

So here are some options I've come up with:

1. Mojito. Limes and mint leaves fit in our color palette, but I always associate this drink with a hot summer happy hour. Does it work at the tail-end of winter/beginning of spring?
2. Key Lime Pie. It's made with lime juice, vanilla vodka, lime cream liqueur and half and half. It sounds fantastic, but really heavy!
3. Apple martini. Everyone loves these, but I hate them. So this is probably a no-go.

Any suggestions?