Thank you everyone for the input.
I had considered a Nikon as there are a larger number of available telephoto lenses, but most are out of my current price range (for the next year or four).
The Spotmatic is also something I've looked at and again it came down to the number of available lenses to suit my needs.
The ME Super looks like something worth considering - it's still within my price range and has lenses in my price range that will suit my needs. I may be sold on it just for the fact that it's lighter than the others. They're all heavier than my Minolta - so lighter is a definite plus.