As an ex-white goods engineer I can say that most washing machines are chosen because of the number of different programmes they offer, e.g. different wash temperatures, rinse cycles, anti-crease, spin speed etc.
I often went to repair both extremes of the spectrum and found that people with the machines with the most options, or the ones with the least, generally only used 2 programmes, the 'Boil' wash and a delicates one. Think about it, how many of the various programmes and options on your machinme at home do you use? My advice would be to go for a simple machine with a spin speed of at least 1000rpm.
With regards to the hard water problem, Calgon that's advertised on the telly really does work, although I'm not too sure about using it in every wash as it would probably work out more expensive than buying a new machine. In South Yorkshire where I live it is soft water and there are a few pockets in the area where the water is hard. I used to recommend to my customers in the hard water areas that they use Calgon once a month or every couple of weeks and wash a load of towels on the highest temperature setting (usually 90 degrees). The towels can take the temperature and give the water a good old slosh around which tends to keep the inside of the machine clean. You could always fit a water softener instead of Calgon, check that out thjough as I have no experience of these.
It's a good idea to wash towels at 90 degs at leat once a month anyway irrespective of hard or soft water areas. As most of the washing done these days tends to be on the 30 or 40 degree setting, bacteria builds up on the inside of the machine, it is Orange in colour and if it gets onto your clothes then it looks like rust which leads people to think the machine is rusty somewhere inside. Pull back the fold on the door seal and you will more than likely find it there. It is the same kind of bacteria you find in bathrooms, usually on the shower head.
Kelvin