I grew up in a house with electric heat and found that it did have several advantages over other heat sources. In my case, we had radiant heat, so there were no radiators or baseboard heaters to interfere with furniture placement. Additionally, a home with electric heat pays an overall lower rate to CL&P for their usage than a home with another heat fuel. Sometimes a buyer's concern with a particular type of heat comes from lack of information. Buyer preferences also often stem from familiarity. Large portions of the country-often in the south-heat with electricity. So, for people moving in from out of the area and with proper complete knowledge, some buyers will decide that electric heat is just fine with them.
My overall philosophy when counseling sellers about making renovations to their home for the express purpose of selling is to only make those changes or upgrades that will sell your house for a high enough price that the increase in value MORE than covers the cost of the upgrade. More often than not, a change will increase the value of the home but not by as much as you put into that change. If you spend $5000.00 changing something for the sale, but only sell the house for $3000.00 more, the change was not worthwhile.
I would hold off on replacing the heating system (unless it is so old that it would need to be replaced regardless of fuel type to function properly). As other agents have said, there are other options to overcoming a buyer's potential objection to electric than replacing the system up front.
Good luck with your sale and let us know if you have any other questions!