Condensing boiler matched with a properly sized indirect are really the ultimate in fuel efficiency and domestic hot water performance. The colder the return water - from heating system or indirect - the more the boiler will condense the by-products of combustion and recover the latent heat trapped therein. Pre-heating well water would raise the potable water entering the indirect-fired water heater thereby defeating the high differential temperature and perhaps shortening the cycle.
At best this is an energy trade. Anything gained by one heat transfer is lost to parasitic energy cost in the next. Regardless, buying an "extra" indirect or even a holding tank to temper well water can not be a good investment. If you want to make a condensing boiler more efficient think about having a factory trained condensing boiler technician tune the boiler for optimum efficiency using a proper combustion analyser and don't forget to have him check the outdoor reset. All high efficiency condensing boilers come with an outdoor sensor and on-board microprocessor that matches boiler temperature to outdoor temperate...in reverse i.e. the colder it gets outside, the warmer the water in the radiation will be.
Modern condensing boiler also modulate flame to maintain water temperature while space heating but also during the much more demanding domestic hot water mode. While making domestic hot water a condensing boiler will normally try to operate at 180°F until the indirect is satisfied. Making it quick and keeping it hot with extra insulation is the flawless strategy that has made all other boiler/water heater combinations obsolete - given a certain class and size building be it new or old.
If your condensing boiler with indirect is set up right you are in better shape than most of the country for space heating and DHW.