After some on bike thinking and a play with Sheldon's Gear calculator (thanks Sheldon), I've decided that I can improve the riding of my 2007 model Trek520 by changing the 30 tooth chainring for a 26 - lots of decent hills here, big heavy me noticing the decent hills, the change would lead to a definite improvement in how the bike works for me (an extra gear and a sensible shifting pattern from middle to small chainring). The 42 tooth middle ring is perfect for my use so I'm not touching that.
The bike is the current model - Ultegra cranks. She's done about 800km so the shop isn't going to consider a 'free upgrade' on the parts and I'm not going to fork out money for a different set of cranks - it's not that big an issue. If I can just change the 30 tooth for a 26, I'll be happier than I am now (which is pretty darned happy).
BUT, my lbs rang their supplier and Shimano don't make a 26 tooth chainring for the Ultegra crank.
Is there an alternative? Or am I just going to have to get stronger?