Replacing 42/52 crankset to 39/52 - will it make a difference?
You asked: will changing the front to e.g. 39/52 setup make a noticable difference?
My answer is an unequivocal 'yes'. If you can however, consider 34 or 36-tooth inner and 50T outer, if you can find chainrings that fit your spider. TA make a large range of chainrings, however new ones will probably cost more than the monetary value of your bike.