In reply to Pete Graham:
We did Don Quixote last year and I was a bit concerned about the descent (had been down it before when it was very icy) so I took lightweight boots and crampons and my partner took just boots. I am glad I did. As it was we abbed down onto the glacier and just had to reascend to the cable for a lift down to the valley (with 5 minutes spare...) My partner and hubby said I was a wuss for putting on the crampons, but it was basically the last steep bit from the end of the abseil onto the glacier proper that I didn't fancy without. It was only 50 metres or so, but it was steep enough and icy. If I wouldn't have had them I would have managed fine, but as I say I was glad I had them.
That said, the people in front of us only wore approach shoes and were fine, just slipping around a bit.
However, if you would have to descend all the way into the valley, I'd definitely want lightweight boots at least.
Now, this is all based on having snow on the glacier, might be a different story if it's all icy. So, maybe find out whether that's the case before setting off and then you can ditch the crampons if it's all soft snow. BTW very lightweight stuff will do IMHO.