The Spark is a fun little car at low speeds, but ultimately it's cramped and under-powered, especially in the torque department (94 ft-lbs at 4400 RPM). You might find it dangerously underpowered at high-elevations.
Is new a requirement? Have you ever seen a Ford C-Max? It's one of my favorite toads. Crossover-ish seating position, 40+ MPG, good handling, reasonable power, and with the Energi model; 15 miles of all-electric range. Towing it 4-down is simple. No special programming or wiring needed (other than rear lights). It even has double tail-light lenses, so one can be converted to dedicated tow-vehicle-powered lights without diodes.
Getting one coming off a 2-year lease will cost less than a new Spark.