Based on quite a bit of seat time with all three fin types....
I want to increase my cruising range, get a better workout and add the sail feature. ...am in pretty good physical condition.
Either the ST or Turbo will improve your cruising range. Both are significantly more efficient than standard fins. The actual cruising
performance between STs and Turbos is not that much. For a given speed, Turbos are not
more difficult to pedal -- you use a slower cadence to get the same speed, similar effort. My reasonably fit daughter pedals Turbos for an hour + without stopping.
Turbos do have more surface area, better acceleration potential, better sprint potential, a higher cruise potential and will give you a better work out IF
you tap the potential. By contrast, the ST fins are similar in resistance to the standard fins -- better efficiency improves the performance.
Both STs and Turbos will improve your sailing performance due to a better daggerboard effect -- Turbos more so than STs.
Is the leg effort really that much higher with the turbos?
Only to the extent you're pushing the boat faster.
Is V1 Mirage drive breakage a real issue with normal use?
Regardless of the fins you choose, you will eventually get a mast wobble and have to replace the sprockets with your "V1" Drive. Turbofins will accelerate this. V2 sprockets have been redesigned to eliminate this problem. I highly recommend that, if
you get the Turbo upgrade kit (turbos and masts), you specify threaded masts (no additional cost) and also order v2 sprockets ($32 for the pair plus installation charge if any). Bcastile's alternate recommendation sounds even more economical for the same end result. You do not need the separate (and more expensive) v2 drum upgrade to accommodate these fins. You do not need to purchase any spare masts, as I seriously doubt that you will ever break one without accidentally bending one several times first.
If you decide to get the STs, you can just buy the fins for now and use your existing components (ST fins use standard masts). You could convert to V2 sprockets, but will have to buy the new masts separately.
It's worth noting ...again...that Drive set-up (lube, adjustment and fin setting) makes a big difference in efficiency and performance. A well operating Drive runs smoothly and freely with relaxed clew outhaul settings (STs and Turbos have the adjustable "outhauls"). This difference can be as significant as fin selection in terms of pedaling effort.