Thanks guys for all your reactions and yes Mr. Zippy, the default Mooney does in fact have visible spoilers/speed brakes but seemingly with no effect when deployed. I went into the Mooney's AIR file and found an entry "Spoilers available = FALSE" ?? I changed it into TRUE and this now does seems to have at least some effect.

However, what I learned from this is that even although most (light) aircraft do not have visible spoilers and/or speed brakes, these can in fact be installed anyway and used to further reduce approach speeds when full flaps and extended gear have little or no effect. However, this will not become my standard practice but only for those aircraft with which I need to dodge hills and trees during already very flat approaches.

Thanks again.