Hi Cecco,
I'm not sure that alternate starting makes a lot of difference. On the other hand, it probably doesn't do any harm either.
As far as regularly turning the engine is concerned; this is definitely a good idea as corrosion will build up in between the stator case and the high pressure compressor blades after shut-down. If not 'polished off' by turning the rotor every 4 weeks or so, this corrosion can build to such an extent that it will eventually seize up the whole engine.
Remember, these engines were designed to be used once only - powering a cruise missile!