Again, a good reason to sign up with Evilution as there is an in depth procedure for removing the drain plug for the motor coolant, and then removing the front radiator lower hose to drain coolant. To refill, there is a procedure to refill and then remove a hose on the motor to let out any air in the system.
Most coolant is good for about 5 years and 50,000 miles I would think your car should be good for a bit yet.
A lot of shops use a machine that the splice into the heater hose line and it draws out the coolant and flushes the system, then refills it. I have no idea if it would work on a smart or not. and if it would take care of the 'bubble' in the block.
I have heard both good and bad about those machines, that they knock stuff loose and end up plugging passages, or that they do a great job cleaning things out. I guess you need to form your own opinion. I would think just draining and refilling would work fine if the system is in good shape, but some sort of cleaning would be better if there was a buildup inside the radiator or block, how would you know?? I guess if you had a core plug come out or blew a radiator, but that would probably be too late for a cleaning.